... and this is how the story started...
:s/foo/bar/gc
replace every foo in a text with bar (confirm after each detected occurrence).
goto beginning of a word (move cursor onto its first letter), type v1ey
to copy that word and move cursor to target word (its first letter) and type v1ep
to overwrite it with copied word (not taht overwritten word is now in clipboard, i.e. can be pastes again - easy word swaps).
Locations you should know: ~/.vimrc
Initially, do this: