Yeah, same question, are you cutting out a circle that you're going to use, or just cutting an opening such as the speaker boxes? If you're cutting a circular piece, you can use a circle cutting jig. You normally would drill a small hole and insert a peg that holds on to the jig. A plunge rounter then makes multiple passes. Since it's a low power router, you will make many light passes and do it without pushing the bit too hard forward.
If you're making some sort of table top, you put the good side down and drill the hole only part way through. Put a tab of tape on the drill bit so you don't penetrate or cause a bump in the middle of the circle's good side.
You do have to work out how to attach the router to the jig. Usually done by taking off the base plate and using it to mark the location of the mounting bolts. Use a punch to mark the center of each mounting hole, it will give you a dimple that will help you drill accurately.
You can use the same small mounting bolds you removed from the base to attach to the jig. If you're using pan head bolts, you can drill slightly oversized holes, then a larger hole part way through so you can position the router on the jig. Here's an over simplified drawing of what I'm saying.
For something like a table top where you're using glued up hardwood, you can use a spiral bit to cut the circle, then put in some sort of roundover or ogee bit to make a nice edge. If it's plywood, you just cut it and use iron on edging.
Once you get started, just take your time. It is really a pretty easy thing to do, just don't try to cut too deep on each pass, usually no deeper than 1/8th inch per pass. The Jig will do most of the work for you. When I do this, I suspend the power cord from something overhead so it stays out of the way. And make sure the center pin is firmly in place. My jig wants a 1/4 inch pin and I often just use an upside down drill bit. If the circle is made of 1/4 ply, I will drill about half an inch deep on the back side.
I am also a fan of using an inch thick piece of insulating foam underneath the workpiece, and clamp the corners down as best I can. You can also use some double sided tape to hold the circle in place. With a couple of strips of tape, if you manage to move it, you're pushing too fast.
Hope this is helpful. These days I cut circles with my band saw, different kind of jig required for that. It's even easier than cutting one with the router. But for cutting a clean circular hole, the router with a spiral bit is the way to go, the band saw won't do that.
Also attached is a picture of four sizes of down spiral router bits. You can use high speed steel for occasional use. Carbide bits are sharper and last longer, but far more susceptible to breaking and heat damage.
The more I do, the less I accomplish.