These are not "verbs". It's a conjugation of a verb "to go" (iku) 行きたい means "want to go" (~たい means "want") So if you want to be polite, just say "行きたいです" (want to go) 行きたかった means "wanted to go" Same situation as above, just add "です" at the end. 行きたくて there's a complicated nuance behind that. It means "I want to go and...". Basicially, "I want to do (something) and (a connotation of something else which is implied)", 行きたくない - Negative form of the above. 行きたかった means "wanted to go" (add "です") I'm too lazy to do the rest, I hope I was able to help you a little. :)