Here are clear instructions on how to measure angles with your hand, taught well and in language you can easily understand and use yourself.
See how I don't distort material cited? See how I support with links to credible sources, which don't contradict my point? See how the instructions I cite from two different sources don't leave crucial information out, like that it is vital that your hand be at a certain position relative to your eye or nothing works. And that this works in real life but not on computer screens, which distort angles and warp flat space to fit it on the screen.
A couple of rules of thumb that will help to apply angles. An object that subtends 1º is 57.2 times further away than the dimension subtended. That means that if a ship were 300' long and subtended 1º it would be 57x300 = 17,100 feet or 5,700 yards away. Objects subtending 30º are twice as far away as they are in the dimension whose angle you are measuring. Objects subtending 45º are as far away as they are long.
I used to use the 45º rule with my sextant, measuring sailboat masts. People hate taking down their mast to measure its height and need to know whether they can get under that bridge. So I would set my sextant at 45º and back up until the top of the mast lined up with the base of the mast. All I had to do then was measure my distance to the mast with a tape measure and that was the height. Took two minutes! To be accurate we add the height from the mast seat to the waterline to get height of the masthead above the water. Sometimes you can't see the mast seat so you can use the cabin top instead.