Difference between 下る,下がる、下りる?

(Kudaru,sagaru,oriru)They all roughly mean going down but im hqving a hard time finding out the differqnce between them by just googling. I know theres also 下げる and an equivalent for 下りる that i dont remember right now but the conversion between the "sister verbs" is easier but it would be nice having an explanation for them aswell. Also if anyone has an answer please tell me if you have like a memory rule or something.

by HD144p