Я так и не решил, стоит ли ставить вазу у окна или лучше оставить её на полке.

Так и не is a very common pattern meaning never actually managed to, still didn’t, or in the end didn’t.

So Я так и не решил means more than just I didn’t decide. It suggests that the speaker was expected to decide, probably thought about it, but the decision still never happened.

A close English equivalent is:

• I still haven’t decided
• I never did decide

Решил is the past tense of the perfective verb решить. Perfective verbs focus on the result or completion of an action.

Here, the speaker means: I never reached a decision.

If you used решал, that would come from the imperfective решать, which usually means was deciding, used to decide, or was trying to decide. That would shift the focus to the process, not the final outcome.

So:

• Я не решил = I didn’t decide / I haven’t decided
• Я не решал = I wasn’t deciding / I didn’t make decisions / I wasn’t in the process of deciding

In this sentence, the missing result is what matters, so решил is the natural choice.

Ли is a particle used for embedded yes/no questions: whether.

So стоит ли ставить вазу у окна means:

• whether it’s worth putting the vase by the window
• whether I should put the vase by the window

This is not a direct question like Стоит ли ставить вазу у окна? although the wording is the same. Here it is embedded inside a larger sentence after решил.

A useful pattern is:

• Я не знаю, стоит ли... = I don’t know whether it’s worth...
• Он спросил, можно ли... = He asked whether it’s possible / allowed...

In Russian, ли usually comes after the word it affects most directly.

So:

• стоит ли ставить... = whether it is worth putting...

You do not normally say ли стоит here.

This placement is very typical:

• знаю ли я = whether I know
• можно ли войти = whether one may enter
• правда ли это = whether this is true / is this true?

No. Although стоить looks similar to стоять, they are different verbs.

Here стоит comes from стоить, which means:

• to be worth
• to be advisable
• to make sense

So стоит ли ставить вазу у окна means:

• is it worth putting the vase by the window?
• should I put the vase by the window?

This is not the verb стоять meaning to stand.

Compare:

• Ваза стоит у окна = The vase is standing by the window
• Стоит поставить вазу у окна = It would be a good idea to put the vase by the window

After стоит ли, Russian often uses the infinitive in a general, non-result-focused way. Ставить is imperfective, so it presents the action as an option under consideration: to put / to place.

Here the speaker is weighing alternatives, not emphasizing the completed result of a single act.

So стоит ли ставить вазу у окна sounds natural as whether to put the vase by the window.

That said, стоит ли поставить is also possible in some contexts if you want to focus more on a single completed action. The difference is subtle:

• ставить = the action as an option, more general
• поставить = the one-time completed placement

In this sentence, ставить sounds very natural because the speaker is simply considering what to do with the vase.

Because вазу is the accusative case, and the vase is the direct object of ставить.

The basic form is:

• ваза = nominative singular

But after a verb like ставить meaning to put/place, you need the object in the accusative:

• ставить что? → вазу

So:

• Ваза красивая. = The vase is beautiful.
• Я ставлю вазу у окна. = I am putting the vase by the window.

The preposition у normally requires the genitive case.

So:

• окно = nominative
• у окна = by the window / near the window

This is just standard case government:

• у дома = by the house
• у двери = by the door
• у окна = by the window

Here у окна describes location.

Because на полке describes location, not motion toward a destination.

Russian uses:

• на + accusative for motion onto something
• на + prepositional for location on something

Compare:

• поставить вазу на полку = to put the vase onto the shelf
• оставить её на полке = to leave it on the shelf

In your sentence, after оставить, the idea is that the vase will remain on the shelf, so the location form на полке is used.

Yes, you could repeat вазу, but её is more natural because it avoids repetition.

So:

• оставить её на полке = leave it on the shelf

Here её is the accusative singular pronoun referring to вазу.

Since ваза is feminine, the pronoun is feminine too:

• ваза → её

Repeating вазу would still be grammatically correct, but it would sound less smooth:

• ...или лучше оставить вазу на полке

Russian often uses pronouns in exactly this way, just as English does.

Here лучше means better in the sense of it would be better to.

So:

• или лучше оставить её на полке = or better to leave it on the shelf
• more natural English: or whether it would be better to leave it on the shelf

Russian often uses лучше very compactly, without repeating extra words like would be.

Compare:

• Лучше подождать. = It’s better to wait.
• Лучше не спорить. = It’s better not to argue.

Because Russian often avoids repeating words that are already understood from the first part of the sentence.

The full logical meaning is something like:

• ...стоит ли ставить вазу у окна или лучше её оставить на полке

The second option is understood as the alternative being compared, so repeating стоит ли is unnecessary.

English does the same thing:

• I haven’t decided whether to put the vase by the window or leave it on the shelf.

We do not need to repeat whether to before the second verb.

Или means or and connects the two alternatives:

• ставить вазу у окна
• оставить её на полке

So the speaker is deciding between two possibilities:

1. put the vase by the window
2. leave it on the shelf

It is a straightforward coordinating conjunction here.

This word order is neutral and natural.

The structure is:

• Я так и не решил = main clause
• стоит ли ставить вазу у окна или лучше оставить её на полке = subordinate clause explaining what the decision is about

Russian word order is flexible, but this version is very standard because it presents:

1. the fact that no decision was made
2. the content of that undecided question

You might move things around for emphasis in other contexts, but the original sentence sounds normal and idiomatic.

Because the sentence contains a subordinate clause.

The first part is:

• Я так и не решил

Then comes the embedded question introduced by ли:

• стоит ли ставить вазу у окна или лучше оставить её на полке

Russian normally separates this kind of subordinate clause with a comma.

So the comma marks the boundary between:

• the main statement
• what exactly was not decided

No, that would misread стоит.

In this sentence:

• решил = decided
• стоит ли = whether it is worth / whether one should
• ставить = to put

So стоит ли ставить does not mean whether it stands. It means whether to put it or whether it would be better to put it.

A more accurate literal breakdown is:

• I still didn’t decide whether it’s worth putting the vase by the window or better leaving it on the shelf.

Natural English would be:

• I still haven’t decided whether to put the vase by the window or leave it on the shelf.