If a UTS session is not already open, open one.
If the session is not currently connected to a host, click the connect button on the toolbar.
Press INSERT.
When the session is in insert mode, INS appears on the status line, and when you type characters on the screen, those characters appear at the cursor location, and all subsequent characters move to the right.
In overwrite mode, when you type characters on the screen, those characters overwrite any existing characters on the screen.