Sprite is called Sprite.
If you pick by the object you pick all the instances, or the first instance depending on the action.
Sprite set angle to 90
If you pick by the object instance variable you "filter" out all the instances that don't match and pick all that do.
Sprite variable myvariable = 1 set x to sprite.x +1
The variable isn't the only way to pick, but it is a standard one.
Instance variables are located in the preferences side after you have selected an instance in the editor, or from the object list on the right.
The starting tutorials should show that very well.