How do I add a new explosion? And how do I edit it?

You need to use Instance.new. This is how you'll do it:

local customexplosion = Instance.new("Explosion")
customexplosion.BlastRadius = --Number
customexplosion.BlastPressure = --Number
customexplosion.Visible = --your choice
customexplosion.Parent = --Put your part, or use workspace depending on some parts
customexplosion.Position = --put your location, ex: game.Workspace.Epart.Position

something like this:

local explosion = Instance.new("Explosion")
explosion.Parent=workspace
explosion.BlastPressure=5*100000
explosion.BlastRadius=4
explosion.DestroyJointRadiusPercent=4
explosion.ExplosionType=Enum.ExplosionType.Craters
explosion.Position=Vector3.new(0,10,0)
wait(1)
explosion:destroy()

it explodes as soon as you create it!!