Where are the two girls going after lunch? Do what? There is no class in the afternoon.
That depends on how old they are. If it is a primary or secondary school student, it is most common for one party to go to the other party's home to play or do homework. It is also possible to go to the park or the library. If you are a college student, you should either go to the library or go shopping. It is common for college girls to go shopping together. Choose clothes and cosmetics, visit parks and watch movies.