See the reference manual section quoted below...
Arranging > Adding Time to the Arrangement
It is often useful to insert a range of silence into an arrangement, effectively adding time to a section. To do this, select the Range tool in the Arrange view, then select a range across any Tracks on which you wish you insert silence. With the range selected, press [Ctrl]/[Cmd]+[Alt]+[I] on the keyboard to insert silence in that range.
Any Events that were in the range where silence was inserted are split, if necessary, and moved to the right across the timeline. If automation data is present, it is moved to follow the Events. Hidden Tracks are not affected, in this case.
If your chosen range of Tracks spans all Tracks in the arrangement, global parameter settings (such as tempo changes, time signature changes, and markers) follow the Events, as well. Hidden Tracks are not affected, in this case.
You can also add time to the arrangement without making a selection. Simply place your cursor at the time in the arrangement that you want the silence to be inserted, and press [Ctrl]/[Cmd]+[Alt]+[I]. A window appears which lets you specify a range of time to insert silence. Hidden Tracks are split and moved just like visible Tracks, in this case.