The Object Instance Variables dialog lists all the instance variables an object type has. It can be opened from the Properties Bar while the object's properties are showing, or from right-clicking the object in the Project Bar or Object Bar and selecting Instance variables....
Instance variables can be added with the toolbar at the top or by right-clicking and selecting Add instance variable. This opens the Add Instance Variable dialog. The toolbar and right-click menu also allow you to rename (F2) or delete (Del) instance variables. Double click an instance variable in the list to edit it.
Instance variables can be reordered by using the Up and Down buttons on the toolbar, or by dragging and dropping them. The order of instance variables is just for organisation - it does not affect how they actually work.
If all instances of the object type have the same initial value for an instance variable, it is displayed in the Initial value column. However, different instances can have different initial values set via the Properties Bar. If there are different initial values across the instances, the Initial value column will display <varies>. Editing an instance variable with varying values and changing the initial value from the Edit Instance Variable dialog will set a new initial value for all the instances, overwriting the previous value for all of them.