The main theme of GraphQL, & the most important thing in this domain is that it makes things very good for a huge App like Facebook, Twitter, Gmail etc.; which have a lot of versions of Clients in the market. Coz there are a Zillion Android/iOS devices say, with different version of OS. & different versions of Apps, Clients.
If you don’t have a huge app, I think others can guide you better with what you should know, & what is important for you to know.
The biggest benefit of GraphQL is that you can virtually type the customized queries you want, when you want, without worrying about the Backend APIs, REST Endpoints, etc. E.g., to have a certain kind to Query interface via HTTP, it has to be built first on the Backend.
GraphQL makes this requirement not necesary. You can type any query & don’t need a backend REST API for it setup in advance. In fact you don’t need it all together.
Work a little with GraphQL Tutorials, and you will appreciate it more.