You don't really need to understand TRS, but if you clicked the link, I'll pretend you are interested. Warning: There may be math.
TRS (Tennis Rating System - aka Todd's Rating System) is a conceptually simple rating system that can be easily interpreted for comparing players.
It starts at 0 for players who have no tennis skill and do not seem to pick the game up easily. Picture someone swinging and missing the ball completely more often than not and almost no ability to get a serve in play.
There really isn't an upper end because it's never been used to rate people above 45, but I think the theoretical cap for Serena and Rafa is about 65. Comparisons to other rating systems are below.
What does a rating mean? It mostly means things when compared to another player. Each point on the system represents a one break of serve margin of victory over someone else. So, if a player rated 35 plays against a 32, the expected result is a 3-break victory - about 6-4, 6-2.
So, every 6 points on the scale represents an expected 6-0, 6-0 victory.
For a frame of reference, using descriptions that are fairly true for Oregon Girls Tennis:
Most of the better varsity teams in Oregon have 1-2 players rated 31-35. The middle of their varsity team is rated about 22 and their lower varsity members are rated 12-15. That is a very wide range.
State champions in Oregon tend to be rated 43-46.
Division III college players range from 29 up to about 41.
Division 1 college players range from 38 up to about 55.
For my local Sherwood-area members, our league's stronger teams are flatter. Most schools don't have anyone who have broken through 28, but they have good depth with lower varsity players being 14-16.
TRS 28 is about equal to the 3.5 / 4.0 NTRP border, which I think tends to be a UTR of 5 (I love the concept of UTR but it is horrible at differentiating players below ratings of 6, especially women).
TRS 22 is about equal to the 3.0 / 3.5 NTRP border