I'm completely new to wireshark. I have Ubuntu on a Dell with wireless connection. When I go to Wireshark Capture Option, I cannot select any interface since no interface is listed. What is the problem and how can I fix that?
You probably should check out the article in the wireshark wiki about capture privileges.
If this is a temporary setup you could just start wireshark with sudo. But this isn't really the best approach from a security perspective.
Also see the capturing on un*x section in the FAQ, it has some other things you should be aware of.
The main problem is in Unix the wireshark is usually run as the normal user so you won't have root privileges, try running wireshark through terminal as "sudo wireshark" this will solve the initial problem