Like on all of these social apps, you have to create your own profile, where you can upload pictures and personal info. In OkCupid you can also answer hundreds of optional questions that let you enhance your profile in order to find better matches.
When you start out on OkCupid you can choose what type of relationship you're looking for and search for profiles that match that. For example, if you're only interested on friendships with people of the same sexual orientation, you can find people that are looking for that as well.
OkCupid is an excellent alternative for meeting people. Like almost all apps of this type, it lets you find interesting people near you, chat with them, and if both of you want to, even get together.