Hmmm... if your talking about looping the item you have (recorded, imported or MIDI), just left click and drag it out to the right and it will loop natively.
This can be turned on or off in Options->Preferences->Project->Media Item Defaults
If you're talking about looping (as in recoding a loop) then there's super8 looper in Reaper that can do this...
Edit: But all these questions you're having could be answered by the User Guide
http://reaper.fm/userguide.php
And I don't mean this like asking questions is bad in any way. I just noticed you have a lot of basic questions and I think the UG could help you from pulling your hair out.
Edit edit: Also, you can use grouping for moving items "synced". Make sure grouping is enabled (there's an icon for it on the toolbar) and all items selected (that you want grouped). Right click and under Group select Group items. Now they move all in a group.
You can also you gluing to glue all the items you want as one item (on a track). Select all items and right click and select Glue items. Note! This will not add fadeins or fadeouts to the items. I'm assuming from your previous posts you're doing some beat sampling. So you might want small fadeouts and fadeins in your items in order to avoid clicks. This gluing can be found in the
Actions->Item: Glue items, ignoring time selection, including leading fade-in and trailing fade-out
Setting up shortcuts will help your life tremendously.