Мы долго искали ключ и всё-таки нашли его.

This is a classic Russian aspect contrast.

• искали is from искать (imperfective): it describes an ongoing process — they were searching, looking for some time.
• нашли is from найти (perfective): it shows a completed result — they ended up finding it.

So Russian naturally uses:

• imperfective for the activity/process
• perfective for the successful result

That is why Мы долго искали... sounds right for we searched for a long time, and ...нашли его sounds right for found it.

Долго means for a long time. It fits very naturally with an imperfective verb, because imperfective verbs describe duration, repetition, or process.

So:

• долго искали = they were searching for a long time

With a perfective verb, долго is usually less natural if you want to emphasize the whole process of searching. The searching itself is ongoing, so искали is the expected choice.

Всё-таки adds the idea of in the end, after all, nevertheless, or despite the difficulty.

In this sentence, it suggests something like:

• the search took a long time
• it may have seemed difficult or uncertain
• but in the end they succeeded

So всё-таки is not just neutral finally. It often carries a sense of despite everything or after all that.

Because ключ here is the direct object of искали, so it is in the accusative case.

For a masculine inanimate noun like ключ, the accusative singular is the same as the nominative singular:

• nominative: ключ
• accusative: ключ

So even though it is the object, the form does not change.

Его means him/it, and here it means it, referring back to ключ.

After нашли, the object is again in the accusative case, and for он / it the accusative form is его.

So:

• нашли ключ = found the key
• нашли его = found it

Russian often uses a pronoun like this instead of repeating the noun.

Yes, it is possible, because the object is already understood from context. Russian often leaves out an object if it is obvious.

But нашли его sounds a bit more complete and explicit. It also helps tie the second part directly back to ключ.

So both are possible:

• Мы долго искали ключ и всё-таки нашли его. — explicit
• Мы долго искали ключ и всё-таки нашли. — object understood from context

In Russian past tense, the verb agrees with gender/number, not person.

Since the subject is мы (we), the subject is plural, so the past tense form ends in -ли:

• искал = he searched
• искала = she searched
• искало = it searched
• искали = they/we searched

And the same pattern applies to нашли.

So мы requires the plural past form.

Yes. Russian often omits subject pronouns when the meaning is clear from the verb form or context.

So you can say:

• Долго искали ключ и всё-таки нашли его.

This can still mean We searched for the key for a long time and finally found it, depending on context.

However, including мы can make the subject explicit, add emphasis, or simply sound more natural in some situations.

Russian word order is flexible. Нашли его is a normal, neutral order.

But other orders are possible, for example:

• Мы долго искали ключ и всё-таки его нашли.

This version puts slightly more focus on его, as if stressing it was the key that we did find.

In the original sentence, the ending нашли его sounds smooth and neutral. Word order in Russian often changes emphasis rather than basic meaning.

They are related in meaning, but they are not an aspect pair in the strictest sense.

• искать = to search/look for
• найти = to find

They describe different stages of the situation:

• искать = the process of trying
• найти = the successful result

A more direct aspect pair for найти is:

• находить (imperfective)
• найти (perfective)

So:

• искать = to search for
• находить / найти = to find

That is why искали... нашли is so common: it describes the process first and the result second.

И simply connects the two actions:

• искали
• нашли

So it means and.

The combination и всё-таки often works like and yet, and still, or and in the end. It links the two parts while also showing contrast or persistence:

• they searched for a long time, and yet / and still / and in the end they found it

So и joins the clauses, and всё-таки adds the nuance.

Strictly speaking, the standard spelling is всё-таки.

However, in everyday Russian writing, people often write все-таки without the dots over ё. This is very common in normal texts.

A learner should know that:

• всё-таки = standard spelling
• все-таки = very common practical spelling

They are understood as the same word here.

Usually долго stays close to искали, because it describes the searching process.

Natural versions include:

• Мы долго искали ключ и всё-таки нашли его.
• Мы искали ключ долго и всё-таки нашли его.

The second is possible, but less neutral. The first sounds more natural in most contexts.

Putting долго next to искали makes the sentence easiest to understand.