If you have, for example, paragraph in a LaTeX file and you want to comment it (so that it does not appear in the output anymore), then you have to insert the percent sign '%' at the beginning of every line. An easy way to do this is to select visually the block of text, press ':' for entering a vim command (which automatically expands to :'<,'>) and to use substitute s/^/%/ The whole command then looks like :'<,'>s/^// So just press enter and the comment will be inserted at the beginning of all the selected lines.