At a hockey game, i walked by this girl, i know her ), she said hey, i said hi back, about an hour later..?

She wants to get your attention. She is flirting with you. A good way to flirt back is to start a conversation with her instead of just saying hi. If you see one another in public or at a sporting event you can say how you like a team or that the cops just ped by and you wonder what it is for. You can also ask her where she is going. If she is going to get a snack you can offer to pay or ask her if you can join her. You can walk her home if you see her on the street or offer to buy a snack or drink, if you are headed to a bar.