First off: I hate P'ing at urinals, and use the cubicle / stalls when available (and clean). Barring cleanliness (stadiums, gas stations and rest stops are the worst culprits...) I will use the urinals as a third resort (If I can't stand in the cubicle for some reason). Now, my 8 year old kid, he prefers to stand to p / use a urinal anytime over standing over a wc or sitting down I assume that's generally the preference for GBs.
Anyway, when I have to "whip it out" generally I pull down the waistband of both pants and underwear with one hand and hold it below the sack, generally just kinda hold that waistband tight against the upper thigh so it doesn't fall down. I then use the other hand to guide the aiming of the stream. Once finished, give it a gentle shake at the base / balls to make sure any leftover drips are out and then proceed to pull pants/undies back up. When shaking be careful to make sure the drips go into the urinal and not on the floor or your shoes (or those of your neighbor in a crowded restroom) which is definitely a danger

Public restroom time is generally time for men to be as disgusting as possible, hocking loogys into the urinal/ floor, rampant flatulence, farmer blowing boogers, and i can't tell you how many people walk by the sinks without a second glance... And there is generally NO TALKING to others except for -- maybe -- a mumbled "excuse me" as you walk too close to others. No looking at anyone else in the eyes, especially
eyes front when actually using the facilities.
If you are using a restroom in a business office / workplace, there are more manners and people generally keep the facilities cleaner, but no guarantees.
I've seen some guys who go "freehand" and lean up against the wall with
both hands on the wall or leaning back with both hands at their waist. I have no idea how they keep their pants from falling to the floor (which always has drips on it -ew) or how they can make sure their aim is in the right place in this position. I wonder if they care. A lot of the more macho-type guys make a lot of sighing, lean back and forth / sway side to side, and other weird gruff "man noises" and mannerisms so you may have to observe to see if any of those mannerisms or vocalizations make sense.