I want to use unwanted milkcrates to create a storage space in garage.

use cable ties to hook them together. you can stack them vertical or horizontal. if you want to put them on the wall , you can use hooks to screw in the wall and hang the crates. Easy Peary!

Easy Peary!

Easy Peazy

First get rid of all that you don't use, keep only what you need, so you have room to park your vehicles in the garage. Use sturdy boxes, you get free at Costco, diaper boxes, many liquor stores will give away boxes, if you want to get fancy, paint them to match, late summer stores like Target or Walmart discount the plastic storage bins with lids, watch for Home Depot to have a sale on metal storage racks, or look for used ones, even a baker's rack would work , you don't have to do all at once, as the boxes are found, utilize them.

Hard to find milkcrate giveways anymore, but if you can get them, I've stacked them using zip ties to hold them together, and fasten to the wall as you would a bookcase with an earthquake fastner to prevent tip over. Put the heaviest stuff on the bottom.

Cable ties are a great idea! I love the idea of DIY garage shelving with milk crates. They would be easy to anchor to the wall too with the hooks so the shelving unit you build doesn't accidentally fall over.

You could connect the crates with zipties.

What is an earthquake fastener?

Great ideas, thanks again.