Everything is relative.
To me, 5% dwm.exe usage is nothing. The other processes are necessary for Windows and must use CPU or Windows won't run at all.
Your system will be dead in the water.
If one has a process using 95%-100% CPU and refuses to let go of the CPU, then that is a real problem. You'll get a freezing mouse, slow loading browsers, choppy videos; in other words, you'll know something isn't right and often a reboot will solve it.
Best advice: Watch and learn via Task Manager, but don't do anything. Else, don't fire up Task Manager at all.