hello all. What exactly is mushroom compost? Simply put, how is it made? How can it be done from home by an amateur?

I grow some mushrooms and when the blocks of mycelium are spent I want to use that leftover substrate for my garden. I just dont know the RIGHT way to do it. And I dont understand enough advanced biology to just pick up a book and get it. So far just experimenting Ive learned:
>trichoderma is the main ingredient in most mychorizae products. Trichoderma is extremely easy to grow. Its almost an inevitable contam for all mushroom blocks
>Top dressing spent mushroom blocks onto old outdoor plants gives them a burst of new life. With indoor plants not so much, can even lend to stalled growth and fungus gnats.