I want to encrypt passwords using the C# WPF. what is the best algorithm (and easy to implement) to use? and I want some example about how to use it ...
Do not try to create your own encryption algorithm rather use the cryptography classes provided in the .NET Framework through System.Security.Cryptography.
For passwords a good solution is to use a oneway encryption like a MD5 hash or SHA1. And when the user enters his/her password you compute the hash and compare it to the stored hash. The advantage of this is that you do not need to worry about how to securely store the key used to encrypt the passwords.
To increase the security of using a one way hash you can apply a salt, this help restrict the effectiveness of certain types of attackes like a dictionary attack etc. I have not read the wiki entry, but I am sure this will provide more detail.