Learn Hardcore Turkish: Lütfen nevresimi yıka.

The -i is the accusative case marker, showing that nevresim (“duvet cover”) is a definite direct object. Turkish uses vowel harmony for this suffix: since nevresim ends in the vowel i, the suffix is also -i, giving nevresimi.

Why is there no word for “you” before yıka?

Turkish normally drops subject pronouns when they’re clear from the verb. The imperative form yıka already implies “(you) wash,” so there’s no need to say sen.

What is yıka, and how is it formed?

The infinitive is yıkamak (“to wash”). To form the familiar singular imperative, you remove -mak and use the bare stem yıka.

Can I move lütfen around? Why is it at the beginning here?

Lütfen (“please”) is flexible in Turkish. It can go at the start of the sentence, immediately before the verb, or even after the object. All are grammatically correct; placing it first is simply very common and polite. For example:
• Lütfen nevresimi yıka.
• Nevresimi lütfen yıka.
• Nevresimi yıka lütfen.

How do I say “please wash my duvet cover” if I want to explicitly mark “my”?