The Insert and Cut icon shortcuts are the insert and delete key.
Insert uses the previously selected rectangle to determine the number of threads to insert immediately before the selected rectangle. Likewise, cut uses the selected rectangle to determine the threads to cut.
When insert is used without a selection, one blank thread is inserted to the right, for warp, and one blank row above, for weft.
When insert with a selection, the number of threads equal to the selected rectangle is inserted to the right for warp, and that number of rows above for weft.
Cut (or delete) removes threads and closes the gap. To leave the gap open and empty, use the shift key.