Important STL's in c++

Guyz, its been 9 months since I started Competitive Programming and I realize that STL is really important.I tried to learn them by looking at past submissions of other people and some googling but couldn’t understand it.Can you guyz please mention sources for learning STL? & are some good resources to learn STL.

Check out this link : Best Resources to learn STL

Try googling topcoder’s stl tutorial.They are awesome.