Hey Cali,
so depending on the software you are using, the method might vary.
When using Lightroom, the software automatically overlays a grid over your image. If you press “O” (o, not zero) on the keyboard, you can switch between different overlays and one of them is a much thicker grid – the number of squares depends on the actual size of your image). Among the various overlays, you also have diagonals and spirals that are excellent to resize 1×1 images.
If you are using Photoshop, what you can do is go open a new file and set it to whatever size and aspect ratio you want (say 1080×1080 if you are going for IG, for example). Then go over to View, and select New Guide Layout. There you can choose how many rows and columns you want and Photoshop will automatically create the grid for you.
Other software might offer different methods. GIMP has a very similar function to Ps, but in general, you should have similar features.