In Ukraine president proposes candidate for prime-minister and parliament accept or don't accept him.
Then prime-minister and president are forming government.
After Poroshenko's win I expect Udar(Klitchko's party) to get some(probably quite a lot) posts in government.
Yatsenyuk will most likely remain prime-minister, he is average politician, but good economist, which makes him good prime-minister in current situation.
Poroshenko claim that his goal is to unite democratic powers and Fatherland is considered to be part of them, so some them for sure will stay in government.