没 has the water radical 氵 on the left — its first meaning was 'to sink beneath the water', to be submerged and gone. From 'gone / vanished' it grew into the everyday negator: what's not there, what you don't have.
没 is the special partner of 有 (which you just learned). 有 (to have) is negated ONLY by 没 — never 不. So 'I don't have' is 我没有, and 'nobody' is 没人. 没 also negates past actions: 我没看 = 'I didn't watch'. It's one of the two great negators of Chinese, alongside 不.
Water (氵) closing over something — it SINKS, it's gone, it's NOT there.
有 is the one verb you never negate with 不 — only with 没. 我不有 is always wrong; 我没有 ('I don't have') is right. 不 and 没 split the whole job of saying 'no' in Chinese.