A product is an offering for an item to sell. Under TeamPlay1 this could be a class like a skills session or a camp, a team membership, merchandise, or a tournament. Note: a tournament is a specialized product so it isn't recomeneded that you edit tournament information here.
Since it is a goal to manage players at "TeamPlay1" when a player is created you must associate a product with the player. You will only be able to select players for your team if they have a "Team" product assoicated with them that is not expired. For the most part you should not have to set a product to a player since that should be done when the parent registers the child for your team, or if you Imported Players.
To manage your products select "Manage ==> Products" and you will get a list of current products. Select the edit button to modify the product. At the bottom of the list there is an option to create a "New Product" or you can go to "New ==> New Product" from the top drop down menu.