Formal:
* Есть (est') - This is the most common and formal way to say "eat".
Informal:
* Кушать (kushat') - This is a more informal and friendly way to say "eat". It is often used when speaking to children or close friends.
Imperative:
* Ешь (yesh') - This means "eat!" and is the imperative form of the verb "есть".
Here are some examples:
* Я ем суп. (Ya em sup.) - I am eating soup. (Formal)
* Я кушаю суп. (Ya kushayu sup.) - I am eating soup. (Informal)
* Ешь суп! (Yesh sup!) - Eat soup!
Hope this helps!