Inside corners also get treated with joint tape. There may or may not be tapered edges here, but it doesn't really matter too much. Slightly uneven walls won't be as visible in the corners as on a flat wall.
First apply a thin layer of joint compound inside the seam and on both sides of the corner.
Measure and cut off the length of joint tape you need. Then fold the tape in half and press it into the corner. Most brands of tape come with a crease in the middle to make this easier.
Press the tape into corner, then run a knife down each side to set it into the mud and to work out any excess mud.
Lightly coat both sides with joint compound again.
The outside corner bead will have a little valley between the metal ridge on the corner and the surface of the drywall. Now you want to fill this with mud.
With mud on your knife, run it down each side of the corner bead. Hold the knife at about a 45 degree angle; it should be touching the wall and the ridge at the corner. Scrape off anything that rises above that level. Clean off any bits of mud left on the ridge.
You should end up with about a 4" wide band of mud on either side of the corner.
Mudding Fastener Heads
The last thing you have to do for the tape coat is to cover all of the screw and nail heads.
It just takes a small amount of mud to cover these, but start by troweling on more than you need. And cover an entire row of screws with one stroke.
Gently scrape off the excess mud with the taping knife almost perpendicular to the surface. This will leave a very thin layer of mud all the way up and down the wall.
The mud over the screw and nail heads will shrink a little, so you'll have to repeat this step with each of the next two coats.
Wrapping up for the day
When you finish the tape coat, you need to let it all dry at least overnight. Clean all your tools real thoroughly. If you have any dried mud left on your knives it'll cause little gouges when you do your next coat.
Throw out any mud left in your pans. Scrape down the sides of the mud bucket, and pour a little water on top of it to keep it from drying out. Pour this water off before using the mud the next time.