The Standard Sphere Grid is what most players should be used to, as it divides the characters into set roles that are separated by Key Sphere nodes. This is great for beginners to the game, as the roles are easy enough to manage and you won’t get overwhelmed. The biggest problem is that the characters are restricted to these roles until much later in the game, when you can start accessing the Key Spheres. Even then, the limited number of Key Spheres you get will still keep characters somewhat glued to their section.
Both Sphere Grids function the same, as you will earn AP from winning battles and upon getting enough AP, you will earn a Sphere Level. You then use these Sphere Levels to move around the Sphere Grid. It should be noted that the Standard Sphere Grid has around 50 or so more nodes on it, when compared to the Expert Sphere Grid. This makes it easier to max out more stats in the end game, especially when taking on the Monster Arena stuff, and optional superbosses.