Mudding is the process of applying wet joint compound to the seams between drywall panels and smoothing it flush with the wall. In almost all cases, you need to apply drywall tape to the seams to reinforce the compound and keep it from crumbling out when dry. Drywall pros use paper tape, because it's fast and offers the smoothest finish, but it can be difficult to work with. Fiberglass mesh tape is more user-friendly.
Paper tape comes in large rolls, and you may cut off as much as you need as you work. To apply paper tape, first fill the seam with wet drywall compound, and smooth it on the surface of the seam. The wetness of the compound is what holds the paper tape in place. Don't allow the joint compound to dry before applying paper tape or it won't adhere. After smoothing the tape in place with a drywall-taping knife, let the seam dry, and then apply one or more thin coats of drywall compound over the paper tape. Do not overlap tape where horizontal joints meet vertical joints.
Fiberglass Mesh Tape
Fiberglass mesh tape is self-adhesive and is easier to work with than paper tape. To use this tape, cut and stick sections of the tape directly over the bare drywall joints. After the tape is in place, taking care not to overlap the tape anywhere, you will apply wet joint compound, pushing it through the holes in the mesh and into the seams beneath the tape. Like paper tape, you'll need to let the seams dry, and then apply additional thin coats of compound over the tape.
You can cut both types of tape with a utility knife. You'll need a tape measure to cut paper tape to the correct length, but you'll apply fiberglass tape directly on the seam, as you unroll it, so no measuring is necessary. Use a 6-inch drywall-taping knife for the initial application of joint compound for both types of tape and switch to a wider, 10-inch taping knife to feather out the edges of the compound. On subsequent mud applications, use only the 10-inch knife.
New Installation vs. Drywall Repair
New drywall construction requires the use of tape for the best results. However, if you're mudding a hairline crack in an existing drywall ceiling or wall, you may apply wet joint compound to the crack with a 6-inch taping knife, and smooth it flush with the drywall without using tape. Cracks wider than 1/8-inch benefit from the addition of drywall tape.