First begin by introducing yourself as a 21 yr. old man. Make sure that you are a secure person (not insecure, because if you are insecure, it will come through and women find that unappealing).
Start going out with friends and networking through them. Also, College....where else are there 1,000 male and females all close in age! Great place to mingle and get an education. Also, don't try so hard, continue with your life and love will just fall into place at the right time.
sorry i didn't answer how to get girls to go on a date....not sure about that, but maybe just keep asking, or go out with groups of friends at this point. maybe you seem to desperate and thats why they say no.
rather than think about getting into a relationship, at 21, just think about dating. ask girls you like to go to the movies or something but don't expect anything more. its supposed to be fun. and you can find out more what kind of girl you like from going out with some even if its just one date. at this point in life you are just starting out. dating is to find out what kind of person you enjoy being with and later think about what you want in a wife and life partner, but not yet. good luck!