In Reaper you can't select a part of the audio item in itself. You're always selecting time selection + possibly item(s), depending how you're doign it. But you can still kind of do that PT style editing in Reaper, it is quite handy eg. if you have to cut out large parts of audio on multiple items at once. If you hold alt while you rclick (and drag), you do get the marquee selection for item(s) + time selection simultaneously. With this you are creating and x/y selection wich you can then cut out. There is an proper action for this too: "Item: Remove selected area of selected items." Lets say you need to edit 15 drum tracks, cut them out for a silent passage or something. Just alt+rclick and drag so that you select all 15 drum items (on y axis) and the time you want to cut out (on x axis). Then hit the above mentioned action and you're done.