Java encryption and decryption

I've been trying to find a good tutorial to teach me how to encrypt and decrypt strings for about an hour now and so far I haven't learned anything... Can some one post a link to a tutorial for me or explain it to me? Thanks in advance

There are many ways to encrypt something, do you know how you wish to do so? The following provides very detailed descriptions of how you can perform encryption using the java cryptography extension library: Java Cryptography Extension

i want to have the user choose a decryption key im not really sure what that is called