I am interested in the multimedia, is it necessary to learn the Maya software suit to enter the multimedia world. I mean for getting the job in the multimedia field, I ask this thing . I don't know Maya.. :(

I work in the Multimedia world and don't know Maya. It's actually pretty uncommon to know Maya.
Maya is a 3D program, and if you work with 3D most of the time you ONLY work with 3D.
3D is not easy to use with other programs, so or you are a 3D artist and don't do other things, or you are a multimedia artist and don't know 3D.

If you are interested in Multimedia you should know Photoshop, Illustrator, Flash or Director. (flash is more common but if you want to make DVD's director is better). I think having some artskills are also very handy, and I believe everyone can learn to draw. (drawing is something else than creating art)

You don't impress a boss by telling him that you know the software, you need to have a great portfolio to show that you know the software, as well as having some great creative ideas. So if you want a multimedia job, start building your portfolio :) Good luck!

I have looked at Maya some time ago, not worked on it, but given apresentation on how it works and someone showing me examples. Is maya the most used application for rendering 3D shots?

As you're interested for a job in multimedia field,you should be familiar with different multimedia softwares.It's not necessary to know about Maya,but knowing it will be a plus point for getting a job.In this field you'll have to work with different softwares,so I think you must learn it.