No particular reference comes to mind--its in all the books I have read.
Two kind of paths---relative and absolute:
Relative (ie from where you are): Lets say you want the "frammus" file:
If it is in the current directory: cat frammus
If it is one up: cat ../frammus
If it is in another directory at the same level--eg "otherdir": cat ../otherdir/frammus
Similarly, to cd to subdirectory "stuff":
Absolute paths always start at root, and list all the intermediate directories, so if frammus is in "otherdir", which is in your home folder (you are "smiley"), then you would get to frammus with:
If you are running executable files, the system will Look in the PATH variable first. You can bypass this behavior by specifying an absolute or relative path. For example, you often see ./command This means run command in the current directory---and dont check PATH.
to see what is in PATH, type echo $PATH
This should give you the general idea---play with it and it will start to make sense.