Requester wrote:

ok now i want to plant bamboo and create a huge forest of them behind my
house. first questino is where do you find them? i have some from a thai
store that i have in water they have roots.

That's draceana, aka "lucky bamboo," not true bamboo. Doesn't do so
well outdoors as true bamboos, which can handle anything from near-arctic
cold to tropical heat.

For true bamboos, try larger, upscale nurseries. Plan to pay. Common
golden bamboo (p. aurea) sells for about $50 per 5 gallon pot, though it
does pay back rapidly if moderately well tended.

You have choices. Aurea grows to 25 feet, tops. If you want that
"huge forest" and have room -- like several acres -- consider the
giant lumber types, such as black or moso. That last one's impressive,
with 6" "trunks" growing a foot per day up to 80 feet or better.

In between are hundreds of varieties, with differences more subtle
than dramatic. Buddha's belly is attractive, with fat, alternating
coke-bottle shaped internodes. Others feature variegated coloration,
similar to tiger stripes.

can i plant them outside? will
2 bamboo stalks create more and more? how do they spread?

They're giant grasses, and spread accordingly. Running types spread
by long underground runners, like lawn turf. Clumping types produce no
runners, so will be better behaved.

Take care with weed killers near the grove. Since (again), the
entire grove is one single plant, dosing one culm doses them all.