Welcome to TFP!
Sounds like a challenge, but it can be done. The first thing to look into is equipment. A pump and filter. If you feel comfortable with fairly simple PVC plumbing and simple electrical connections, this is certainly a DIY job.
Any idea how much water the pool holds? poolcalculator.com has a feature to figure the volume from the length, width and average depth. That info is needed to choose the pump size required.
You also need to decide what kind of filter. There is an article in Pool School about the different filter types. During the cleanup process, a sand filter will be the easiest to deal with while the water is really dirty.
You are also going to want a pool leaf rake, which is a net that can be used to remove leaves and other crud from the bottom of the pool.
Once you have circulation going, then you can start adding chemicals to clean the water.