Start off with a cube as your base
Add a cylinder that with act as your top
Then copy paste the cylinder three more times so that they are the same size
Then connect them together making sure that the cylinders are on top of the cube
Then choose the colour you want and colour it
Next you will want to go under and extrude part of the cube then adding a cylinder extruding the middle of it so that you get the design of a lego
Then you will add a smaller cylinder extruding it to make the holes and then copy pasting another three more thimes to get the same results
Next you will need to add a cylinder and cut it in hafl to make it thinner, do this seven times rotating it to fix the sides
Using the colour you chose earlier, now and all you have to do is make it darker
This is how you make a lego cube :)