@ Karim - You don't list what version of Moodle you are using so I'm just going to link you to the 2.x guide on importing questions into the question bank.
@Yossi - Without seeing an example of this file that was sent to you, it is hard to make a recommendation on your situation. You will probably have to break the large file down into smaller files for each purpose though as Moodle doesn't have a way to do all that you need in one shot.
For example, take all the users to be created and put them in their own file. You could then upload users from CSV file. Not only can you have Moodle create the users in this file, you can also have it enroll them in the necessary courses and put them in groups.
Happy
oodling!
