For a girl to become your girlfriend, you need to do everything in stages.
First, get to know each other and start a conversation. Then chat for a while and get to know each other better and inspire confidence on the part of the girl in relation to you. Then a very important point - the first date. How you spend it will depend on whether you will meet later or not. If everything went well, then a couple more meetings and you can confess your feelings to the girl and tell her that you want to build a serious relationship with her.
Congratulations, you will have a girlfriend after completing all these steps.