I know the intel letters but not AMD. Also is it normal for my CPUs clock speed to go down when idle and to go up when under load?
If you mean r3 vs r5 vs threadripper, the names just describes levels of performance/price/the audience the specified cpus are made for. So r3 is like budget, r5 gaming, and threadripper's for different sorts of workstations.
It's similar to intel's naming scheme. In fact, I would argue AMD's is less vague.
& Yes it's normal for the CPU to do that, it has boost clock so that when the cpu needs more power, it can get it.
For Ryzen, G suffix as in 2200G indicates an included graphics unit (AMD calls it an APU).
X suffix as in 2600X indicates extended frequency boost, ie. higher "turbo" clock boost.
The other two covered most of it. The letters are for quick identification of the products target level. Most CPU's will lower their clock to save on power and lower heat output, which can slow fan speed, making it quieter.
G - Integrated graphics
X - Higher overclocks available
That's pretty much it.