is there any way to create a course which should be first of all taken by students after registration and they cannot subscribe(or see) other courses until they pass this introduction course?
well you could password protect the other courses and only allow them the password once they have satisfactorily passed the first course - that might be the simplest way to go about it. And if you didn't want manually to have to tell them the password you could include it in a quiz or lesson they need to do as the very last activity on the initial course.
well its a very simple solution but it will be too confusing for students and protecting everything with a password is not a good way too 
((
maybe smth else?
maybe smth else?
Actually passwording works quite well for us. Teachers can easily change passwords as necessary. The password is only need to enroll in the course. Once enrolled, the student no longer needs the password.
Here's an idea:
The required course would not have a password necessary for enrolling.
Another option would be to have an end of course "assignment" that emails the facilitator or instructor for the required course and that person can check progress through the required course and then send back the password or even enroll the student in the next course by using "assign roles" in that course.
Paula Clough
I have like 200+ courses... that won't work for me now