The Superhero Database Classification number, or SHDB Class, is a number that represents the overall 'power' of a character. All traits of a character are used for calculating the Classification.
What it DOESN'T mean
This doesn't mean that a higher class would always beat a lower class character. But the bigger the difference in Class is, the more obvious it is who'll win in a fight.
How is this calculated
( INT^1.3 + (STR*0.5 )^2 + (SPE*0.5)^2 + DUR^1.6 + (POW + (SPS*SPL))^2 + COM^1.8 ) ^ TIER
Super Power Score and Level
Every Super Power has a score (SPS) that is used to calculate the Class. Each Super Power also has 3 levels (SPL). The level is set when connecting that Super Power to a character. The level determines the final score, of the Super Power, being used in the calculation.
She Like earth
galactus kills superman
Think of it this way; Superheroes like SpiderMan, Iron Man, Batman, Wolverine, etc are of a different level than regular humanity.
The gods and similar beings (Thor, Hercules, Wonder Woman, Silver Surfer, The Eternals, Captain Marvel, Elders of the Universe, etc) are of a level that far above "normal" super beings (Superman is roughly in this range. he's managed to beat Thor but it took all he had to do it).
Above those powerhouses are their Leaders - Beings like Zeus and Odin - Odin can, and has, simply took Thor's power away from him. Zeus has done the same with Hercules. I'd guess Phantom Stranger and Maybe the Guardians of the Unverse fit here.
Above these beings are entities -beings that the Asgardian and Olympian Gods call Gods. Death, and Eternity (essentially Life - the opposite of Death, manifest as a being) consider Galactus their brother. Thanos often manages to get powered up to this level when he's trying to detroy the Universe (he has a thing for death and believes that if he killed everyone, she'd have to recognize him. I'd guess Darseid around here at times also.
Galactus doesn't really feel physical discomfort a*except his all encompassing hunger) and physical attacks, at most, cause problems with his outfit - which is actually a containment suit he uses to help localize his power. If it tears, it would take some time to regather the energy and repair the suit. So, Superman, could theoretically manage to get past Galactus with such a maneuver. If punctured; controlling the massive amounts of power unleashed...read giant explosion! would be difficult. This wouldn't hurt Galactus, but would destroy the solar system he happened to be in at the time. And most likely Superman, if he was still close by.
But, he doesn't need that kind of outlay of power anyway - Galactus can transmute elements. He could turn...everything around him into green kryptonite at whim.