>>77995890worth noting if you're new:
combat level is sort of like an average (not exactly but close enough) of all of your combat skills (attack, strength, ranged, magic, hitpoints, defense, and prayer)
Increasing any of these will increase your combat level.
Attack influences chance to hit (melee), strength influences max hit (melee), ranged does both for ranged, magic unlocks spells and increases accuracy, hitpoints is hitpoints, and defense decreases your chance to be hit (both magick and defense are used for magick defense)
If you have too low of attack you will literally be unable to hit anything, and it also is the main stat used to unlock new gear tiers for melee weapons. It's really important early on. also NEVER train your combat stats with split exp (you can select which skill you're training in the combat tab by hovering over the icons)