Mix the drywall finishing mud according to the instructions on the container. If you have a pre-mixed bucket of mud, you merely need to open the bucket and mix the already moistened mixture within the container until it is ready for application. With dry mix, you need to add an appropriate amount of water (dependent on the size of the bag and manufacturer) and mix it.
Scoop some mud from the mixing container into your handheld mud container. Fill it as full as you can comfortably hold in your off hand. Move to your working area and scoop some mud out of your handheld container with a flat trowel. Place the mud against the wall and spread it upwards with the trowel. Work your way from the floor up.
Spread the mud around the wall to create your mud texture. There is no right or wrong way to do this, as you can move the trowel in any direction you choose, and you can apply as much or as little mud as you want. Experiment until you are comfortable with the final result. Scoop more mud on the wall as required, and use different sized trowels for different finishes.