Examples of Search and Replace in Vim

Replace all spaces with new lines (in the current line only):

:s/ /\r/g

Replace "%3A" with ":" and "%2F" with "/"

:s/%3A/\:/g
:s/%2F/\//g

If substitution consists from more than one step and is used frequently, it is easier to use a hotkey for that. To map the substitution above to the hotkey "-r", add into .vimrc:

let mapleader = "-"
map <Leader>r :s/%3A/\:/g<CR>:s/%2F/\//g<CR>