I am making an application which is a Twitter client. This means it connects to Twitter with OAuth. I register my application to Twitter and got all my keys, but now I do no
If the full OAuth web redirection is not convenient, you could try to use Twitter's xAuth service method to just convert a set of Twitter credentials to an OAuth access token (do that once, and save the token). Much easier on mobile applications, but you need to ask Twitter for permission to use xAuth by emailing api@twitter.com.
You could also check out another question on StackOverflow for more information on this.
If your problem is how to actually implement OAuth interactions, you might want to check out OAuth library information on Twitter and/or documentation on the library you are already using.