Sentinels are basically superhumans and guides help them stabilize their energy (or mental power) so that they don't go crazy or die. In some works, sentinels can only receive proper guiding from a guide of the same or higher level. For example, a B-level guide won't be of much help to an S-level sentinel because the guide is much weaker. Other works also use the concept of "exclusive guide" since the guiding is considered to be sensitive and intimate.
Unlike omegaverse, in guideverse there is almost always some conflict (in the background) that necessitates the existence of sentinels. Maybe there are dungeons, interstellar war, etc.
I forgot to say that guiding is always done through physical contact. I have not read any works where the guide doesn't atleast touch the sentinel/esper's hand or wrist. That said, the more intimate the act, the deeper/better the guiding (this doesn't apply to all guideverse but used a lot for smut reasons).
Most guides I have seen are bottoms but there's a famous one here where the guide is the top so check that out if you're interested.
Can someone please explain the guide/sentinels aus to me? Because when I think sentinel it's like,, a funny robot with a gun. Also why is omega verse not good enough for some people smh.