"The house has a big door"
Translation:Nyumba ina mlango mkubwa
it means has, but only when the thing that is "having" (to the left, in this case the house) is a singular N class noun.
see the table here for details: https://en.wiktionary.org/wiki/wa_na
(in this case ina is the "N class inflected singular present affirmative" of kuwa na)