Is the -en form of a verb always the general form as in this sentence as well?
Yes, most German verbs in the infinitive (i.e. without any conjugations) end with -EN. There are, as ever, a few exceptions, some of them are "sein" (to be), "rudern" (to row), klettern (to climb)...
Nicht here means "Do not"?
Yes, in this case "nicht" means "do not."