Bonsai is a horticultural style, not a cultivar or a ten minute you-tube.
Your juniper is in a landscape pot. It can live in that pot for a couple years if watered at need.
You need all of the following if you want to train it to a shallow bonsai pot.
a wooden chop-stick
pot with large-ish drain holes in the bottom, some screen to cover those holes
bonsai soil or cactus mix
an outdoors space for your juniper to live (on a table or bench is nice)
to read by book or internet on how others train their junipers.
Your not going to transplant until next April or May, so you have time to get used to checking moisture in soil with that chopstick.
Rule # 1 Dry chopstick, its time to water. Damp chopstick, its time to wait (check daily)
Rule # 2 pick up your tree daily, to note problems, If your tree is taking on water properly, weed as needed, and fix in your mind how your tree is growing. Do this as you have your morning cuppa and cigarette.
You can look a tree and draw a scetch of how to prune it a hundred times, you can un-prune it never. As you rummage on the internet or through your library, with top pruning in mind a veritable torrent of photos, should bring you back to your trees and a pad of paper.
Take your time, you are going to live forever, right? So you have all the time you'll need to get the horticultural needs of your tree met, as well as training hopes.
Take the time to understand why a tree should only take one 'insult' a year. (and your tree has already had its quota)