To insert a control in your form, simply drag a control from the control panel and drop it into desired location in the form view. In the UI Designer, there are constraints on where a control can be dropped:
All controls can be dropped into the cells of a Table, Repeating Table or Panel.
The Table, Repeating Table or Panel can be directly dropped into the form view.
The Repeating Table cannot be dropped into the repeating row of a Repeating Table.
The Table and Panel can be dropped into a Repeating Table.