Q: I have just finished SLC. I do not know what to do now. Should I take bridge courses?

​No. In fact computer classes and language classes can be useful.  But you should ask yourself are you really interested? Or are you going because your friends are going?
A lot of students take bridge courses after their SLC just because that is what everyone does. Parents are happy that their kids are 'studying'.  Bridge course institutes are happy that your parents are paying the fees, and you are happy as you feel you are not just sitting home doing nothing.  Many students do not take bridge courses seriously.  They mostly bunk those classes and go to the classes just to ‘kill time’ and to hang out with friends.  You don’t lose much by going, right?  After all, the course material in these courses will be parts that you have already studied or will naturally study later in high school.   So, you just go, what’s the harm?
If you are going just because everyone else is going, and you do not know if you are really interested in the course being taught, I would highly discourage you from joining bridge courses.   Sure, you need to prepare for what comes next in your life.  You should do research on your own, or with a group of friends.  All that is useful because you are an active learner in those classes.  In bridge courses, you just take in passively what is taught to you.  This may teach you a bad habit.
In conclusion, bridge courses are useful only if you have an active interest in the course.  If not, you are better of finding a more productive way of using your time.