A kick-up is a trick where you use your foot to kick an object up into a juggling pattern. The reverse of a kick-up is a foot catch. There are several ways to do kick-ups:
Start with an object on top of your foot and some more objects in your hands. Start juggling, using your foot to make the first throw.
Start with a ball held between your feet and some more balls in your hands. Use your feet to throw the ball up behind your back by jumping. Then start juggling, catching the ball you threw with your feet and adding it to the pattern.
Start with an object on top of your foot while you juggle. Start throwing in the pattern you would use for one more object, and when one hand runs out of objects to throw, use your foot to lift another object up to that hand and add it to the pattern.
Start with an object on top of your foot while you juggle. Throw the other object up with your foot and start throwing in the pattern you would use for one more object (or change the pattern and then throw the object with your foot - the timing to use depends on how many objects you're juggling and how high you throw the object from your foot), catch the object you kicked up and add it to the pattern.
Step on the end of a club to flip it up into your hand.
Juggle, catch one of the objects on your foot, and then use your foot to throw it back up into the pattern.
Juggle, let an object fall down below hand level and collect the rest of the objects, kick the object back up, and start juggling again. You can kick an object in front of you using the inside of your foot, farther in front using the top of your foot, out on the side using the outside of your foot, or behind you using the bottom of your foot. (That last type of kick, invented by Gene Adams, is called a blind kick, a heel kick, or a scorpion kick.)
Juggle, let an object fall down below hand level and kick it back up into the pattern, but keep juggling the whole time, temporarily switching to a pattern with a lower number of objects while you do the kick.
Balance an object on your face, make it fall down behind you, and blind kick it back up over your head and into a juggling pattern.