*
Matches any group of 0 or more characters.

?
Matches exactly one character.

[...]
If you enclose some characters in brackets, the result is a
wildcard that matches those characters. For example, [abc] matches
either a, or b, or c. If you add a ^ after the first bracket, the
sense is reversed; so [^abc] matches any character that is not a,
b, or c. You can include a range, such as [a-j], which matches
anything between a and j. The match is case sensitive, so to allow
any letter, you must use [a-zA-Z].

Expansion patterns are simple once you see some concrete examples:

*.txt
This will give you a list of all filenames that end in .txt, since
the * matches anything at all.

*.[hc]
This gives a list of filenames that end in either .h or .c.

a??
This gives you all three-letter filenames that begin with a.

[^a]??
This gives you all three-letter filenames that do not begin with