The way I did mine was, I drove 4 t-posts in the ground, and ran 4 strands of galvanized wire across the posts. I placed the wires about 12" apart, and the posts about 6' apart.
Then as the vine grow I wrap them around the wires. Blackberries take 2 years to grow fruit. The first year they grow canes, and the second year those cane produce fruit and then they die, and the plants
grow new canes next year.
If the new canes touch the ground they will take root, and next year you can cut them loose and have another plant
At the end of the year remove last years canes, and wrap this years canes around the wires. You may not even need the wires.
I have 1 Apache, 2 Chester, and 2 Black Satin plants