FPS - is how many times engine can render your scene per second. If you want to limit FPS you can look this topic limiting frames
Delta Time - is how much time passed between two last frames.
In my opinion FPS restriction is bad practice because on different hardware FPS can less than you intended and game will be slower than needed. With using delta time you simply can do something like my_character.setX(my_character, my_speed * globalClock.getDt()) and your character would have the same speed independently of FPS.