How can i start a conversation with a random girl and ask for her number ?

IM really in need of a girlfriend and am out of school and everyone at my work is really old like 40 50s IM 18 almost 19 and am feeling lonely I haven had a gf in about 7 months and I want to find one bit don't know how to start a conversation with a random girl like lets say I was at gas station Like 7 -11 or at home what do I say to start a conversation Like last week I was at home depot looking for a paint to put on a bile IM restoring and saw this girl but I didint know what to say to her and she was right next to me also if you don't catch them looking at you is that an indication there not intrested in you