Bottom line, if you are questioning why you should get married, don't do it.
If you are a minor, you will find many legal hoops to jump through. The laws are written this way because statistically, most teenagers who marry end up divorced.
If you have decided that marriage is for the two of you, then check out your locale's requirements. Some still require blood tests, waiting periods, cash only for fees, and more. Some states are requiring some premarital education, which we highly recommend even if it isn't a formal requirement by your community or church.
For a marriage to be long lasting, a couple needs love, commitment, communication and problem solving skills, fidelity, honesty, ability to handle conflict in a constructive way, respect for one another, realistic expectations, understanding, kindness, and a sense of humor.