This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
a wildcard represents something unknown or undefined.
As a basic example we use '?' to represent a single character and '*' to represents zero or more characters
So test?.txt matches test1.txt testA.txt but not test.txt or testAB.txt
test*.txt matches everything test?.txt matches and a bunch more.
Learn by doing. Regular Expressions are all about matching patterns and make extensive use of wildcards.