Games like minecraft uses what is called a texture atlas, a texture atlas is a single image file that contains all the textures needed in the game and stitches them together, uv values are mapped as 0 and 1 so in order to use a specific part of the image the uv values for each vertex needs to differ
For example, say your texture atlas contains 4 textures in a 2x2 matrix and you want to use the top right texture for your blocks, the uv values for the top right texture needs to be (0.5, 0.0), (1.0, 0.0), (0.5, 0.5), and (1.0, 0.5) as no matter what size the image is the uv coordinates are mapped into 0 and 1