Thanks, Glen and Rosie! both of your comments help a lot. I totally understand now.

Hi there, the comment before by Glen Gray is correct but the usual use of this phrase is to make fun of an awkward silence. They even use it on cartoons such as The Simpsons to make fun of a long silence or absence of content. So yes tumble weed is simply a dry plant that is carried by the wind in the dessert but the use of this in conversation is usually meant as a joke about there being a lack of conversation.

It's kinda hard to know without more context. The tumbleweed is a common image in movies or pictures that depict the southwest US, especially cowboy movies. The tumbleweed is a green plant while it grows, but then it dries up and breaks off of it's roots. At this point it is just a big dry ball of sticks.Since it is a ball, it can easily be pushed around by the wind. This would be the meaning of "Tumble." If you have seen a cowboy movie you will sometimes see a tumbleweed roll through a deserted town. Or often when two cowboys have a duel (when they face each other and shoot, and one dies) a tumbleweed will roll between them . That neither of them notices the tumbleweed shows how concentrated they are on the duel. So my guess would be that maybe a person is in a place where they shouldn't be, and somebody is telling them to go home by using this tumbleweed reference.