I dont know how they came to exist in this manhwa, but the company is just a way to organize everything and play people for their abilities, espers are paid to use their powers, and guides are paid to help espers. Esper's powers are like toxin to their body, the longer they use, they become more instable mentally and physically. Guides have a "tranquilizer" effect in espers, their powers help espers regain they rationality like a "filter" to espers toxic powers.
Now about ranking thing about quality and strength. A weaker esper is going to be at a lower hank, and a stronger, with more useful powers is going to be at a higher rank. And for guides is about the quality of their guidance, a low rank guide cant filter much of espers powers and get tired more easily, but high rank guides are the opposite, they have more strength to keep guiding for longer times and the quality of their "filter" is better too.
(Hope this helps)
Story is interesting, still don’t understand the whole concept though, so ‘guides’, essentially, also have ‘superpowers’ cuz else wtf is that ‘guiding’ thing they’re doing, it wasn’t explained fully, and how did they get the ability to do that and why is there a rank to them. They said that espers started losing control or whatever so ml’s dad created the company thing, but did guides already exist then and it was just a place for them to come to guide espers