Перед сном мне пора бы убрать со стола пластилин и альбом, чтобы утром в комнате был порядок.

Because перед normally takes the instrumental case when it means before / in front of.

So:

• сон = sleep
• перед сном = before sleep, more naturally before going to bed

This is a very common Russian expression. Literally it is before sleep, but in context it usually means before bedtime.

Because пора is used in an impersonal construction in Russian.

Russian does not say I am time or anything like that. Instead, it says something like:

• мне пора = it is time for me
• тебе пора = it is time for you
• нам пора = it is time for us

That is why the person goes into the dative case:

• я → мне

So мне пора убрать... means it’s time for me to put away...

Бы makes the statement softer and more nuanced.

Compare:

• мне пора убрать = it’s time for me to put it away
• мне пора бы убрать = I really should put it away / it would be about time for me to put it away

So пора бы often suggests:

• mild self-reproach
• a feeling that this should already have been done
• a softer, less blunt tone

In English, depending on context, it can sound like:

• I should probably...
• I really ought to...
• It’s about time I...

Because пора is followed by an infinitive to express it’s time to do something.

Pattern:

• пора + infinitive

Examples:

• Мне пора идти. = It’s time for me to go.
• Нам пора спать. = It’s time for us to sleep.
• Мне пора убрать со стола... = It’s time for me to clear the table...

So убрать is not conjugated here because it depends on пора.

Because убрать is perfective, and here Russian is talking about a single completed action: getting the clay and album off the table.

• убирать = imperfective, process / repeated action
• убрать = perfective, complete the action

In this sentence, the idea is not to be in the process of tidying, but to put these things away completely so the room is orderly by morning.

So perfective убрать is the natural choice.

The preposition here is basically с = from, but Russian often uses со instead of с for easier pronunciation.

Since the next word starts with ст-:

• с стола is awkward to pronounce
• со стола sounds smoother

So:

• со стола = from the table

Also, after с/со meaning movement away from a surface, Russian uses the genitive case:

• стол → стола

They are the direct objects of убрать, so they are in the accusative case.

However, for many inanimate masculine singular nouns, the accusative looks exactly like the nominative.

So:

• пластилин → accusative пластилин
• альбом → accusative альбом

That is why they appear unchanged.

If these were animate masculine nouns, you would often see a different form.

In Russian, альбом can mean several related things, depending on context:

• an album
• a sketchbook
• a drawing pad
• a scrapbook

In a sentence with пластилин and a child’s room or activity implied, альбом most likely means something like:

• drawing pad
• sketchbook

So the sentence is probably talking about putting away children’s art materials.

Чтобы introduces a clause of purpose or desired result.

Here it means:

• so that
• in order that

So:

• ...убрать со стола пластилин и альбом, чтобы утром в комнате был порядок
• ...put away the clay and sketchbook so that the room is tidy in the morning

This is a very common structure in Russian:

• сделать что-то, чтобы... = do something so that...

This is a very common point of confusion.

After чтобы, Russian often uses the form that looks like the past tense, even when the meaning is not past.

So:

• чтобы был порядок does not mean so that there was order
• it means so that there would be order / so that things are orderly

This is normal Russian grammar after чтобы.

So although был is formally a past-tense-looking form, in this construction it expresses a desired or intended state, not actual past time.

Because порядок is a very common Russian noun for order, tidiness, neatness.

So:

• в комнате был порядок literally = there was order in the room
• natural English = the room was tidy / the room was in order

This is an idiomatic and very common way to speak in Russian.

It focuses on the state of orderliness, not just cleanliness.

For example:

• У него на столе порядок. = His desk is tidy.
• Надо навести порядок в комнате. = We need to put the room in order / tidy up the room.

Because утром is a standard adverbial form meaning in the morning.

It comes from утро and is in the instrumental form, but learners often just memorize it as a time expression:

• утром = in the morning
• днём = in the daytime
• вечером = in the evening
• ночью = at night

So чтобы утром... means so that in the morning...

No preposition is needed.

Yes, Russian word order is flexible.

This version sounds natural because it presents the time and place first, then the resulting state:

• утром = in the morning
• в комнате = in the room
• был порядок = there was order / it was tidy

Other orders are possible, for example:

• чтобы в комнате утром был порядок
• чтобы порядок в комнате был утром — much less natural in most contexts

The original order is good because it flows naturally and emphasizes the desired situation by morning, in the room.

Literally, it is closer to before sleep, but in normal English translation it is often best understood as:

• before bed
• before going to bed
• at bedtime

Which one sounds best depends on context.

So in this sentence, Перед сном мне пора бы убрать... could be understood as:

• Before bed, I really should put away...
• I should probably clear away the clay and sketchbook before going to bed.

That is usually the most natural interpretation.