imasu is a verb:
- imasu ka? (Are you there?)
- hai (Yes)
In English it would be "exist", I guess. I's used for only people and animals.
imasu is also it's used in present continuous tense.
Verb in -te form + imasu
Kaite imasu (I am writing)
Utatte imasu (I am singing) - you probably know it doesn't have to be "I", it can have another omitted pronoun
Whereas "desu" is not a verb on its own, it's auxiliary verb.
sou desu (Right. Literally "it is so")
Merve desu (This is Merve)
Yokatta desu ne (That's nice. Literally, "it was nice")
Omoshiroi desu (It's interesting)
And;
doko desuka? (Where is it?)
(anata wa) doko ni imasu ka? (Where are you?)
NAYOsan ga imasuka? (Is Nayo san there?)
Merve san wa kono heya ni imasu ka? (Is Merve san in this room?)
iie, Merve san no heya wa asoko desu. (No, Merve san's room is there)