Well, I generally ignore everything on the right side, until I know I have a finished recipe, and it's nice to see how much I'm NOT paying for ejuice. But for just regular use, I usually ignore all that pricing stuff.
Also -- I never add water or PGA, so that line stays blank. If you use high-VG, you might want to add some of either, or both, for thinning, but it's not necessary otherwise.
All the rest should be fairly self-explanatory; just enter what you want to target for nic level and PG/VG at the top, and enter each item along with any nicotine they may contain, and their PG/VG level -- actual DIY flavors (not juice) are usually 100% PG; the juices you enter as flavors could be anything, and the program takes everything you enter into account, so you know how much of what to combine.
Andria