Learn Hardcore German: Sie geht langsam in die Stadt.

In German, Sie (capitalized) can mean both she or the formal you. The context (talking about someone going to the city) makes it clear here that it means she. If we meant they, it would typically appear in plural contexts or references to more than one person.

Does geht mean walk or go?

Geht comes from the verb gehen, which can mean to go or to walk. In general contexts, gehen means simply to go by foot, but it can also be a broader way of saying to go somewhere in German, not necessarily specifying the mode of travel.

Why do we say in die Stadt instead of zur Stadt?

In die Stadt literally means into the city, focusing on entering the city area. Zur Stadt can occasionally be used, but it suggests heading more generally to(wards) the city without as strong a sense of entering it. Using in die Stadt emphasizes that she is going inside the city limits.

Where should the adverb langsam be placed in German?

Adverbs in German often appear after the verb or before the verb, depending on emphasis. Placing langsam after geht (as in Sie geht langsam in die Stadt) puts a normal emphasis on the manner in which she goes. You could say Langsam geht sie in die Stadt if you want to emphasize the slowness more strongly.

Could we say Sie läuft langsam in die Stadt?

Yes! Läuft (from laufen) also means walks/runs (depending on context). In everyday German, laufen often just means walk rather than run. So Sie läuft langsam in die Stadt would be acceptable, but it may slightly change the nuance from a more general goes to a more definite sense of walking.