airflow, as in drafts, winds, turbulence.
here's a leet ass diag i drew you.
pink is your electrode
blue is your filler - around 15-20* for normal welding. if you are using a lay-wire technique the wire shallows up alot as you press it downward into the joint and run over it.
orange describes the throat height (thickness of the throat of your weld) its minimum size is equal to the smallest thickness of your base metals - in your case the pipe, not the flange
red shows you what your torch angle can become when walking the cup. you MUST be careful if you let your cup-walking angle slip too shallow like this. the distance between the electrode and the material becomes very small and you will have cross-contamination - assuming you don't drag the electrode into the puddle!
the best thing to do is to eyeball what you are doing then lay a triangular speed square/angle finder into a joint. what most people find out is that their eyeballed angles are a good 20-30* off when they are starting out and it can trip them up.
90* between the filler & torch, eh, depends on what you are doing. you're not going to see 90* between the torch & filler under the helmet welding so dont worry about how that works out.
work on angles, and having the correct positioning. (not just what angle you're working on but WHERE exactly you're working at)