If you have never juggled before, you might want to start with something easy – like handkerchiefs/scarves. Then try with soft foam balls. If you can find a partner, you could try team juggling (pass objects back and forth while juggling) or even juggling in synchro.
Once you get good at juggling, you can try adding in some spins or flips as you have your objects in the air.
Once you learn the basics of juggling, you can get into sync throws, the vamp.. which when put together makes "the box". So start getting your basics first before you get into the tricks. Vamping is really neat, so try that trick! Alternate and don't drop the balls. Once you got that, just start with 2 straight throws starting and stopping. Then you can link more together until you can do it fluidly and confidently. The instructor is throwing them low, but it may help to throw them higher but still controlled. This may give you a little more time. So you can do high with control or low with speed.
practice a 4-2-3 pattern and then you can enter the box pattern. These are some complicated moves, so try some very basic juggling until you get good at that and then experiment with the more advanced combos.