Step 1 is make a grinder and power it. You have a few options here, depending on what you prefer:
A Gasoline engine can power it perfectly, and is the cheapest route to take metal-wise, even if you include the required fermenter and DC engine. This does, however, have the disadvantage of requiring you create and input fuel every once in awhile, requiring a decently large sugar cane farm. (You could also use leaves, which are more efficient, but of course those require shears. HSLA steel shears are best if you want to go that route.)
Alternatively, you can also use 3 shaft junctions to combine the outputs of 4 steam engines, which will provide the same amount of power as a gasoline engine but is more expensive and requires more set-up. This requires a pump on top of a 3x3 of water and powered by a DC engine, some liquid pipes, and either burning netherrack or a lava source block and a cooling fin per steam engine. This option has the advantage of being completely free and infinite power, so all you have to do is leave everything running, plop in whatever you need ground and it will get ground as long as the chunk is loaded.
This route also has the disadvantage of being very loud...
Once you've made this, then step 2 is to make and power an extractor, which isn't easy...
EDIT: I forgot to mention, placing ores in a grinder allows you to triple your ore yield, which is why it's step 1.