Я купил груши и бананы на рынке, а потом ещё взял кефир.

I bought pears and bananas at the market, and then I also got some kefir.

Breakdown of Я купил груши и бананы на рынке, а потом ещё взял кефир.

• я: I
• на: at
• купить: to buy
• и: and

Questions & Answers about Я купил груши и бананы на рынке, а потом ещё взял кефир.

Why are купил and взял used here, not покупал and брал?

Because the sentence describes completed, one-time actions in a sequence:

• купил = bought (completed)
• взял = took / picked up / got (completed)

These are perfective past-tense forms. Russian often uses the perfective aspect when telling what happened next in a finished chain of events.

If you used покупал or брал, that would be imperfective, which usually suggests:

• process,
• repetition,
• background action,
• or an action without focus on completion.

So this sentence sounds like a short finished story: first I bought fruit, then I picked up kefir.

Why do купил and взял end in -л?

That is the normal marker of the past tense in Russian.

In the singular past tense, Russian also shows gender:

• купил, взял = masculine speaker
• купила, взяла = feminine speaker
• купило, взяло = neuter subject
• купили, взяли = plural

So Я купил... tells you the speaker is male. If the speaker were female, it would be Я купила груши и бананы...