Databases are inherently difficult - or impossible - to "secure", simply becuas ethey must be read by applications - which means that if you encode the data, the application has to include the decode information, often as part of the connection string.
And that means that you effectively publish the decrypter with the encrypted data!
While some measures can be taken, they are way beyond the little text box we have here, and can't be implemented without very careful study of the data, the level of protection you need, and the application which will access it. This is not a field where enthusiasm is any substitute for knowledge and experience!
Start here:
Database Security: An Essential Guide | IBM[
^] and when complete, move on to Google to refine your knowledge. But do not expect this to be a quick job - it's likely to take weeks or months before you will know anywhere near enough to actually start protecting anything instead of leaving gaping hole you aren't even aware could exist! Some of it is seriously counter intuitive...
For example, have a look at this:
Password Storage: How to do it.[
^]
While it isn't directly relevant to what you are trying to do, it's an explanation of why what seems like the optimum security solution - encryption - is a very poor security mechanism for passwords.
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