The two accounts won't mirror each other exactly.
But they will to a degree.

One toon follows the other.
You can interchange which leads and which follows.
You can also move the follower independently, via hotkeys to almost stack.
They won't move that far, stacked.

You can have both melee Interact With Target, while Click to Move is engaged.
You could have two ranged classes, each fire the same spell (by putting them on the same hotkey).
Or you could play different classes.

The basics are:
a) Slave follows the main; and
b) Slave assists the main.

There are infinite variations.