So you can interchange the meaning of "going" and "walking" for this one?
”Gå” typically means ”walk”, i.e. does not have the same meaning as ”go” which is used for general motion. Swedish often uses ”åka” where English uses ”go”. But there are some contexts were ”gå” means ”go”, but here, I would translate it as ”walk”.
It is very typical for English speakers to directly translate it as "go" every time - I usually have to think about the context!
Can I use promenerar intead of går? do these words have the same meaning(walk) in the sentence?
They are occasionally interchangeable, but far from always - promenera is more like taking a stroll.
"Att vara på väg" specifically means that someone is on the way somewhere, as in at this very moment. "Att gå" when you have a specific destination in mind is more akin to leaving. It can technically mean you're on your way somewhere as well, but you might want to add something to the sentence to clarify that. "Han håller på att gå till dagis." "He is (currently, in the process of) walking to kindergarten."