Grid based, turn based, movement system

I'm new to unity and programming in general (I have an excellent understanding of the rules of programming, I'm just not completely fluent with the syntax and lexicon yet). I'm making a turn based, grid based, tactics RPG, heavily inspired by Final Fantasy Tactics. I'm in the very beginning stages and while I understand that trial and error is a critical part of the learning process, especially with programming specifically https://speedtest.vet/ https://vidmate.bid/ (I have a background in web development), I'd just like to at least be on the right road if i'm going to be falling over!

My question is in the movement system. Every player will have a speed and jump value between 1 and 10. For each 1 speed they have, they can move 1 square(same for jumping). A diagonal move would count as moving 2 squares. How do I use the Navmesh (I think I also might need to use Ray scattering as well, but i don't fully understand all that) to highlight the area of valid movements based on their speed, jump, and map boundaries/objects. I was wanting to use this system as the movement controller as well. When they click on the highlighted square, the active character moves there.