Can someone help me with this issue I'm having?

I'm 21 yrs old, and i've never been in a relationship. I'm really shy and everytime i go out i see some cute girls but I don't know what to say or do. I tried to talk to some girls in the past and I've been shot down everytime. So how do i get over this? So maybe could you ladies give me some advice on how to make the first move. What makes things worse is I'm a custodian for a living how do I get a girl to be interested in me w/o looking past the fact of what I do for a living. There is a girl that I know who is single also maybe I could get some help with that.