The TikZ manual a large beast, with a huge amount of information. You have to know where to look. It seems that what you want is mostly Part III
"TikZ ist kein Zeichenprogramm", which describes all the tikz commands and for each of them, it lists the basic options, with explanations. It is divided into sections, for example there is a section on drawing paths, that describes the
\draw command, and it lists and explains the main options that apply to the path.
On the other hand, it does not list all the options available to "\draw", for example it does not mention the fill or decorate options, that are described in different sections. Then there are options that are only available when certain libraries are loaded, and you will find those in the discussion of the libraries. As far as I know, there isn't one place where you would find a list of all the options available for a given command or environment.