How to convert a C# application to WebPart in Sharepoint2007??

I'm starting with Sharepoint.

I have a simple C# application using a database. I need to show it in Sharepoint2007, and my boss told me that I have to do it with a WebPart, but I've been looking for information and I haven't found it, I only found how to create simple webparts, but the problem it is that I have the C# application created.

Thanks for your help.