When you "put off" something that you're supposed to do, it means that you wait to do it later. People often put off doing things that are boring, difficult, or stressful.
You can use the phrase "put ___ off" by itself:
A: Have you bought Renee a birthday present yet?
B: No, I've been putting it off.
Or you can use the phrase "until ___" to express when you will or have started doing it:
Don't put off doing your taxes until the week before they're due.