I'm pretty new to working with files In cortex, and I was wondering how do you make an explosion either: Bigger, or do more damage? Specifically for the darkstorm or coalition rocket launchers.

Either add more damage particles.
Or increase the sharpness of the particles.

To make an explosion larger, you could also increase the lifetime of the associated particles, emitters or gibs. This won't necessarily increase the damage it causes to it's target, but it will make it look more impressive.
Dragon's nailed it, increase the sharpness of the particles, the mass of the particles or the number of particles spawned by the explosion.

thank you very much.

Well, not really on the sharpness and mass. If you have more sharp particles, sure, more damage will eventuate, but more terrain rape will as well, and if you dont boost the number of particles, you're still going to have the same max damage due to the way CC's wound system works. Also, since a beginner is very likely to be using grenade fragment MOPixels, which are plenty sharp and heavy enough for just about any vs. vanilla job (seriously, have you seen a base.rte frag grenade go off in someones face?), i'd say go with more particles, and/or secondary explosions (ie particles (likely MOSRs or emitters) with sharp gibs and a low gibimpulselimit, and either a low lifetime (looks patchy), a burst that makes them gib after x ms (fiddly, oldschool), or a lua script to do the same thing (easier).
One could also have a script on each particle that makes it make more particles randomly, to simulate more dangerous fragments (this is how "more powerful" guns are made, mostly), by inflicting more wounds.
Also, for making the explosion more impressive, you'll want to use some fire effect MOSPs and maybe some emitters, not just make it shoot more of everything.
Wow, there you go, an essay on how to make an explosion more dangerous and a postscript about making it pretty.

You can also make a bullet that has many particles but 0 spread, and then they will act like one large bullet.

oh, also, in response to the making it larger, you'll want to increase the velocity.
what the balls cambio, he's talking about an explosion..