The shortcut
Select the file in Finder and press ⌥ ⌘ C. The full path, such as /Users/you/Documents/report.pdf, is now on the clipboard.
The menu
Right-click the file, hold ⌥, and Copy becomes Copy “report.pdf” as Pathname.
Drag into Terminal
Drag any file into a Terminal window and its path is typed for you, with spaces escaped.
See the path
View → Show Path Bar shows the folders at the bottom of every Finder window. Right-click a folder there to copy its path or open Terminal at it.
Go the other way
Copy a path and press ⇧ ⌘ G in Finder to jump there. NotchMind, which I make, recognizes a copied path and offers Reveal in Finder right away. See actions for what you copy.
NotchMind