Okay, now that I've seen a video and got an idea of your situation, firstly, I want to confirm, has the chain been shortened to the shortest available, with the tensioner off?
So no tensioner connected, chain shortened to the shortest possible (you'll probably end up one or two links long to fit the master link back on).
If no, you will need to do so. If yes, the roller on the tensioner, put that up to the top of the tensioner and screw it tight. I don't have lock tight, but I've tightened mine so much I struggle to unscrew it, so I leave it; amazing I didn't cross thread which is good.
Then, pull the bike so that the top of the chain is tight; the bottom will still be loose.
Then, push the tensioner as far up as possible to the rear sprocket and the lower chain should tighten up.
Tighten it all up and you're set.
My chain is a little loose because I heard you don't want to make it too tight as it'll damage it quicker or something.
You'll definitely notice my tensioner is right close to the rear, as most people's are, with the wheel at the top. I didn't put it completely at the top to loosen the chain a bit, as mentioned before.