I understand making useful posts will earn merit but what it means?
I will suggest you to check all the replies here where many of our community members are trying to help you. Its the first thing which could bring merit for you. For getting merit there is no straight way but if you spend your time to help others like everyone is trying to help you by providing proper information's and guidelines then you will be able gain it very soon. Merit is one kind of award and you have to build yourself appropriate for getting this from others. At the very beginning stage of your forum journey its important for you to learn about this forum rather than running after merit.
You can follow below things;
# What is allowed here ?
# What is not allowed here ?
# How the forum works actually ?
# What you should follow before posting a new topic in any section ?
# What kind of post can be helpful for forum users ?
# How you can make your contribution for the forum ?
# How can you help other forum users ?
If you can build yourself properly for making quality posts and contributions then getting merit is just a matter of time.