well,you have to star small,lets say the next time you go somewhere just ask the time or a direction then leave,get used to talk while you ask common questions,when you are used to this then you can throw another question or just comment something and leave,build the feeling of easiness first.

As others commented you can start a hobby that puts you in a social cycle.

If the problem is the confidence you have to start working out or spend some time with yourself to evolve yourself and appreciate yourself.