In terms of find a resource that is free for a certain project- you can see their availability in the People planner.
Simple click on "People" and the perhaps add a filter for the type (using role or tag) :
Then you'll see everyone's availability- scroll to determine the time frame of your project to see who is free:
Once you have determined who is available, you can assign or transfer the assigment to them. To transfer, simply click the 3 dots at the right end of the assignment and click on Transfer and select the available resource.