What does "have down" mean? Something like "understand"?

Native speaker’s answer
Rebecca
To "have [something] down" is similar to "understand!" You're right! It's to be knowledgeable or proficient in something so that you can do it well. It can also mean to have written something down. Ex: I have the presentation down. So I'm ready to present it today. Ex: She's got the whole process of coding down. Ex: I've got it down on my notes here.