The steps are:
1. The user registers, providing user name and password.
2. You hash the password.
3. You save the user name and password to the database.
4. The user logs in, providing user name and password.
5. You hash the password .
6. You query the database for a record with matching user name and password hash.
7. If you find a match then the user is authenticated, otherwise they are not.
The first thing to do is to make sure that you can hash data. You would most likely use the SHA1 or MD5 algorithm. For examples, you should search online for the SHA1Managed class or the MD5CryptoServiceProvider class. You should probably read the documentation for each first, which will most likely contain examples.
Note that hashing and encryption are performed on binary data, i.e. Byte arrays. As such, you will need to convert your password text into Bytes first, you would do this using the Encoding.GetBytes method. Once you have hashed the data, you can either store the result in the database as binary or else convert it to a String and store that. For the latter option, use Convert.ToBase64String.
If you're using MySQL, you should also download Connector/Net from the MySQL web site. It is a MySQL-specific ADO.NET connector.
