Translation:He does not open the door
Yeah, it's good to remember it like -u- = un-
With open and close, I was getting them mixed up for a while because I kept forgetting which one is the inherent one (ie. do you close and unclose doors or open and unopen doors?) but I'm comfortable with it now. I'll still probably mix them up though because I often mix up opposites in any language, which is a bit weird and I wonder what's going on in my brain.
In the present tense (and only in the present tense), the verb end “-a” changes to “-i” in negated verbs.
Check out the Negations chapter in the excellent 2Seeds Swahili course: