^^ Calm down, man.
I'll try and answer your question clearly: Spending zeals to raise HP will increase your combat level. Ever time you gain HP 4 levels, your combat will raise by 1. However, the advantage of spending zeals is that you do not have to gain any combat exp in the SW minigame, as long as you bandage players or bury bones (which doesn't give prayer exp).
For example, if you trained your account in SW using bone burying, you will not gain any exp at all. Say you spend enough zeals to get HP from 72 to 80; you will have gained two combat levels for this. The advantage is that you will not necessarily get any other combat exp; getting this ~1m HP exp using normal combat means you'll have a "collateral" exp gain of ~3m in one of the primary combat skills. Using zeals allows you to get that 1m HP exp with no "collateral" exp gains.