First day of using blog

I have no idea what a blog it is
and I don't know what it can do for me
Writing my own diary or expressing some opinion?
Or even Making some friends with others?
If some one can tell me what a blog really for, I will be very gladed.

My new semester has begun about a week ago, now I have to be ready for those challenges!
good luck for me, I will make my own career!!!

and I can speak a little spanish!!^0^