When someone started with a bitcointalk profile, they want to upgrade their forum rank. That's why merits are very important. You need merits+activities to upgrade your bitcointalk rank. You can find how much merits+activites need to upgrade bitcointalk rank in this official thread
Merit & new rank requirements.
The merits are given by random forum members to your valuable posts. They have to see how important your post give a merit. Then you have to try to make valuable posts on here. You can help someone's question, you can participate in a thread and share your ideas, make some good threads with your knowledge etc posts can get merits.