Regarding Verbs With Irregular Past-Tense Forms

I once assumed that I could form the past tense of any verb simply by adding ed. I now understand the complexity of the English language; for every rule there are exceptions. And while most verbs in the past tense end with ed, many do not.

Figuring out which verbs are regular and which are irregular will take time. I get the impression that something is funny about "do" and "have." At any rate, I know for certain that the past tense of "sleep" is "slope." For example: "I slope with my socks on last night."