You might get more answers if you move this post to the programming section 
. I don’t know how familiar you are with programming, c++ or blueprint, but there are several data types to help you out. Usually a grid is stored in a vector, in this case a 2D vector of integers would represent a grid (think of chess, where one row is A B C etc and the other 1 2 3 etc), each square on the board is a unit on one axis on the vector. Next you define a grid size, such as “100” which could be 100 cm per unit (think of minecraft blocks would be 100x100x100 on a location on the grid). With that in place, you can say “my character moves from position 1X1 to 1X2” which is very similar to chess. to actually move it a few units, you would use the “SetActorLocation” node on a class deriving from AActor and set it to (grid position) X (grid units), in the given example (1X2 with 100 units) you end up at position X:100 Y:200. If none of that makes sense you should first start learning the basics of blueprints on the web, Matthew Wadstein has a great channel on youtube.