most games use an 8x8 grid leading up to 16x16, 32x32, 48x48, 64x64, etc...
you can make tiles in any pixel program in the world, so long as you can move a selection or at least copy the canvas. in paint, just make a 16x16 square and color it whatever your base color will be for that tile. for example if you plan on making grass, you simply make a green 16x16 square and begin drawing on it. once you think you're finished with that tile, select it, hold control, click and drag it to make a duplicate image, and move it down. do the same again and move down to the second one you made, not the first, because you may mess up causing you to make some fixes, which get annoying. so move your two out of three (leaving one up above) next to eachother, select both of those now and move those down connected to the first two. you'll end up with a 32x32 square using 4 tiles. so sorry if you couldnt understand that. anyway, good luck.
