I'm very new to dynamics crm, so I'm sorry if the question is a little bit basic.
I created solution. and added 2 entities - questions&answers.
In questions I've 2 roll up fields, one for the average of all the grade fields in answers entity, and the other for calculate how many answers there are to a question.
How can I create the roll up fields? when I click edit, the Realted entity and the Aggreation fields are empty, and I can't add them nothing.
Considering your setup something like below.
Question(Entity) has many Answers(Entity) i.e 1:N relationship. You could have your relationship as N:1 or N:N as well, Provided you have relationship between Question and Answer entity.