You need to be matched with a user to be able to message them. For a match to happen between 2 users, they both have to like (swipe right) each other's profiles. Both you and your match receive a notification upon the match and can start messaging to get to know each other!
PS - you can also send a one time message to your potential matches by using our Notes feature. Read more about it in our VIP section of the FAQs.