Turning Your Green Swamp Back into a Sparkling Oasis has instructions for you.
First thing you need to do is get a proper test kit. Skip the article in
Pool School and just go order a
TF100 with XL option, since you'll be using a lot of the test powder during the shock
process. May as well get a speedstir, too, and save on shipping. You'll like it.
Then, get a leaf rake - it's like a skimmer but it has more of a bag to it, and use that to clean out as much debris as you can. In the meantime, read
Pool School and some of the success stories in the forum. Like this
recent thread.
Once the test kit arrives, run a full set of tests to decide if a partial drain is needed to reduce CYA buildup.
Then begin the Process.
Dumping massive quantities of bleach and/or "shock powder" without knowing the water chemistry will likely leave you frustrated and broke. And the pool will still be green. The test kit seems like a big outlay, but it will pay for itself.
Do not rely on the pool store tests. Besides inaccuracy, they're really only there to sell you products.