Don't worry about the O2 tank if this is your first brew. When the wort is cooled, just pour it at a good height into the fermenter to make it splash around a lot (obviously, don't spill any on the ground).
Put the lid on. If you don't have a solid stopper, lay some plastic wrap over the lid hole and push the stopper (w/the airlock hole) in to seal it. If you do have a solid stopper, use that instead. Sit down and lay the fermenter horizontally across your thigh. Rock it vigorously left to right for 7 minutes. Set it down, remove the plastic wrap (or solid stopper) and insert and fill the airlock.
You should get perfectly respectable results from this. Take it to the next level some other day. I did 13 batches this way and they were fine. I started using O2 for the last couple batches and honestly there isn't a ton of difference. It cut my lag time in half, sure, but my lag time was generally only around 16 hours to begin with, but I use large starters.
Using a yeast starter is much more important than using O2, in my limited experience. After I began using stir plate starters, I've had to use blowoff tubes instead of airlocks or my fermenters would explode.