I take it you already know what the verb "to walk" means. "Walk" can also be a noun referring to a single walking session e.g. "I'm going for a walk" and "How was your walk?".
"Gait" can only be a noun that refers to how someone walks. By looking at someone's gait you might be able to figure out their gender, age, level of athleticism and if they've recently had any leg or hip injuries. You can also change your gait - you can walk normally, power walk, march, run slowly or sprint. Unless you're a doctor, artist, graphics designer tracker, you probably won't need to use the word "gait". The word "gait" reminds me of various documentaries I watched when I was young, which talked about how we think dinosaurs walked, how we think humans evolved to walk upright, how people had to approach the Pharoah with the left foot forward at all times etc.