To select a single budget item, click on it with the left mouse button. To select more than one item, press the left mouse button and drag. The red selection rectangle will expand to include other cells, but you can only select cells within a single section.
To move items, press the right mouse button within your selection (red selection rectangle) and drag it to the place where you want to insert the items. A green indicator line will appear and show the current location. When you come close to the top or bottom border of the logframe, it will scroll up or down. Release the right mouse button to insert the items you selected.
Another way to move items is to use the Move Up and Move Down buttons in the Lay-out ribbon tab.