Grids and Tracking

So, I've been on a break for a bit and I've finally decided to come back as I still have some projects I want to complete. My current goal is to make a RTS type of game. To do that I need to find a way to the enemies go to a specific target in the shortest path possible. The first thing I though of was to create a grid and using the grid find the path. The problem I'm running into is on how to create that grid. Then I also have no idea on how I would create the tracking systems. I saw that there was a RTS path finding demo by KimsGames though I also don't fully understand its concepts. I'll still be searching for to make it but if I could get help on understanding the concepts behind how the grid is made and how the tracking happens that would be great.