Когда мне хочется чего-нибудь простого, я беру крекеры и делаю тост с сыром.

Мне хочется is a very common Russian way to say I feel like... or I want... in a more spontaneous, less direct way.

• я хочу = I want
• мне хочется = I feel like / I’m in the mood for

Grammatically, хочется is an impersonal form, so the person experiencing the feeling goes in the dative case:

• мне = to me

So the structure is roughly:

• Мне хочется чего-нибудь простого = I feel like something simple

It sounds natural and conversational here.

After verbs of wanting, especially with vague or indefinite things, Russian very often uses the genitive:

• чего-нибудь = something / anything / something or other

This is especially natural with хочется. It gives the sense of wanting some kind of thing, without naming exactly what.

So:

• хочется чего-нибудь простого = I feel like something simple

If you used что-нибудь, it would not be impossible in all contexts, but чего-нибудь is the more idiomatic choice here.

Because простого agrees with чего-нибудь, which is in the genitive case.

Here is the idea:

• чего-нибудь = genitive
• therefore the adjective modifying it must also be in the genitive
• простого = genitive singular

So:

• чего-нибудь простого = something simple

Even though простого looks like masculine/neuter genitive, here it matches the neuter idea of что / something.

Here простого means something like:

• simple
• plain
• not fancy
• easy and uncomplicated

In a food context, it suggests the speaker wants a basic, easy snack rather than a full or elaborate meal.

So чего-нибудь простого is very natural for:

• something simple to eat
• something plain
• something easy

Because Когда мне хочется чего-нибудь простого is a subordinate clause introduced by когда (when).

In Russian, subordinate clauses are normally separated by commas from the main clause.

So the sentence is structured like this:

• Когда мне хочется чего-нибудь простого,
  я беру крекеры и делаю тост с сыром.

This is the same basic idea as English:

• When I feel like something simple, I take crackers and make cheese toast.

Because Russian uses the present tense for habitual or general repeated actions, just like English can.

This sentence does not mean the speaker is doing it right now. It means:

• Whenever I feel like something simple, I usually do this.

So:

• я беру = I take / I grab
• я делаю = I make

This is a general routine or typical reaction.

Because the sentence describes a repeated habit, not one completed future action.

• брать, делать = imperfective
• used for regular, repeated, habitual actions

If you switched to perfective:

• возьму
• сделаю

that would sound more like on one future occasion I will take / I will make.

So in a sentence beginning with when(ever) and describing a usual pattern, the imperfective is the normal choice.

Yes, literally it is I take crackers, but in natural English the meaning is closer to:

• I grab some crackers
• I get out some crackers
• I have crackers

Russian брать is often broader than English take. In food contexts, it can mean you choose or get something to eat.

So here я беру крекеры sounds very natural.

Because крекеры is the direct object of беру, so it is in the accusative plural.

For inanimate plural nouns, the accusative form is the same as the nominative:

• nominative: крекеры
• accusative: крекеры

So the form does not change.

Because Russian has no articles, and it often leaves words like some unexpressed when the meaning is clear from context.

So:

• я беру крекеры can naturally mean
  • I take crackers
  • I grab some crackers
  • I get the crackers

The exact meaning depends on the situation. Russian usually does not need a separate word for that.

Yes, тост can also mean a ceremonial toast as in a speech, but here it clearly means toast as food.

Why is it clear?

Because of the food context:

• крекеры
• с сыром

So делаю тост с сыром means something like:

• I make cheese toast
• I make a toast with cheese

No Russian speaker would think of a drinking toast here.

Because the preposition с meaning with takes the instrumental case.

• сыр = cheese
• с сыром = with cheese

This is a very common pattern:

• кофе с молоком = coffee with milk
• хлеб с маслом = bread with butter
• тост с сыром = toast with cheese

Yes. Russian word order is flexible.

This version is natural because it starts with the situation:

• Когда мне хочется чего-нибудь простого...

and then gives the usual action:

• я беру крекеры и делаю тост с сыром.

You could change the word order in some ways, but this version sounds smooth and neutral. It puts the emphasis on when this feeling happens.

So the current order is a very natural way to say:

• When I feel like something simple, I grab crackers and make cheese toast.