The correction of this poster made me laugh:
It’s a pair of words that can cause confusion. For some people the confusion comes from the pronunciation.
Lose is a verb that is pronounced with a long /u:/ sound (it rhymes with shoes and news). It finishes with a voiced /z/ sound.
Loose is more commonly an adjective and native speakers often pronounce it with a shorter /u:/ sound (it sounds more like goose or spruce). Its last sound is an unvoiced /s/ sound.
Perhaps the easiest way to remember the different spelling is to think that ‘lose’ has lost an ‘o’.