guyathome74 said any company is going to try and promote their own products which are not useless as someone mentioned
Sorry, but 90% of the stuff they try to sell you at the pool store is complete crap.
All you need to keep your pool clear is:
(1) Bleach (for chlorination);
(2) Borax (to raise pH);
(3) Baking soda (to raise total alkalinity); and
(4) Muriatic acid (to lower pH); and
(5) A good test kit.
Lowering total alkalinity is a bit more complicated, involving lowering the pH to between 7.0 and 7.2 and aerating until it rises a bit, then repeating, as needed.
You may need calcium at startup. You will also need stabilizer (cyanuric acid) at startup, but the crap tabs that the pool stores will try to sell you to chlorinate your pool are also in large part made of stabilizer. Using them regularly will quickly raise the CyA levels way over range and severely limit the usefulness of chlorine as a sanitizer, which leads to a green algaeatic mess.
NEVER NEVER NEVER use anything other than more chlorine (bleach, probably the simplest, "shock" being just another word for chlorine/chlorinate) to clear out an algae bloom. Most people underestimate the level to which chlorine needs to be raised/kept to get rid of algae but shock shock shock and filter is by far the best way. Other products either won't work and/or will leave you with all kinds of residues you really don't want in your pool.
If you do it right, you'll never get an algae bloom at all. I've had two pools for a total of about 8 years and have only had algae once.
Again, use the forums and stickies at troublefreepool.com and poolforum.com. They also have very helpful forums on pool repairs, construction, equipment, etc.