Hey TeedaBlackdog, like all native grasses, its important to know where you are wanting to plant it and what is already growing there. Main thing with planting native grasses is seed depth and competition. If you have alot of warm season exotic grasses in tame pasture, then you need to kill if first with some glyphosate. Sometimes it takes several doses to get the job done. Not only do you need to kill the exotic grasses like bermuda or johnson grass, but often you have to deal with a seedbank; especially with johnson grass.
If you are planting in pasture, once the warm season competition is killed gamagrass seed can be drilled in with a seed drill or native grass planter. Unlike other native grasses that can't be planted more than 1/4"-1/2" deep, gamagrass and its big seed can be planted a bit deeper, but no more than 1" Shoot for that 1/2" - 3/4" range. I've planted the seed with a two-row corn planter and it works pretty good.
Gamagrass can also be planted by seed if in small areas. Just find bare areas with no competition and plant no more than an inch deep. You can also dig up gamagrass rhizomes in the winter and plant them as well. They work good, but do like adequate spring moisture to get them going well. Around here, gamagrass will grow in full sun, but I find that it likes partial shade way better. Also, don't burn it when getting established. The rhizomes are pretty close to the top of the ground, and I have found that even a cool winter burn will set it back some.