What does "This won't do" and "This will do" mean?

Native speaker’s answer
Rebecca
"This won't do" means that something is unsatisfactory. On the flip side, "This will do" means that something is satisfactory. The phrases are slightly formal in tone. They work well for someone who's in charge of something. Ex: This venue will do just fine for the wedding reception. Ex: This won't do. The venue is a mess. Ex: This'll do. Thanks for organizing the presentation, Jenna.