To secure the waste canvas to the item being stitched, you'll need to hand baste. It's a good idea to do so beginning in the center so your canvas doesn't pucker or slip. Some stitchers baste every so-many holes from the center out to the edges, while others baste an x from one corner of the waste canvas to the other, starting in the middle. I know basting can be a pain, but you'll find it worth the extra time. If you choose to use interfacing, it can be basted inside the item at the same time you baste on the waste canvas.
Some stitchers do, while others stitch in the hand.
It was pointed out that knit items like sweatshirts and tee shirts can stretch easily, and maybe a hoop wouldn't be a good idea in this case. You'll need to consider what kind of needle you want to use when you stitch with waste canvas. You'll need a sharp needle to penetrate them. The needle that works best for me is a chenille needle. It's sharp, and it has an eye large enough to accommodate multiple strands of floss.