Broken down, it means:

. matches any character except a newline
* matches whatever precedes it (in this case the ".") 0 or more times.
? matches as few times as possible.

So .* acts a lot like a wildcard when you need to match a variety of possible strings, however, it's greedy, so if you're trying to match

(b)text(/b)

in a string that contains

(b)something(/b) and (b)something else(/b) followed by (b)this(/b)

because it's greedy, it will match from the first (b) all the way down to the last (/b). Make it lazy, and .* only matches as little as possible till it finds something that'll complete the pattern, such as the first (/b) instead of the last one.

For the sake of this post, pretend that all ('s and )'s are ['s and ]'s, because I'm apparently too retarded to figure out how to display them without having them parsed.