To bumble is to move or speak in an awkward, fumbling way. You might bumble your way through your first dance performance, tripping over your own two feet.
When you bumble, you walk unsteadily or speak with a stutter. You can also bumble something, or completely mess it up. An inexperienced teacher might bumble her attempts at managing a huge class of middle school students, and you might worry that you'll bumble your first interview as a radio reporter. Bumble was first used in the 1500's, and it's probably an imitative word, or one that sounds like what it means.