Use the "Update" function. Pass in the username, password, text and the output format you require.
Do note that the Yedda Twitter API wrapper uses the old username+password authentication of Twitter which will get deprecated. I suggest that you move to use the OAuth based Twitter API which is MUCH more secure for your users since it doesn't require them to pass you the username and password.
You can post on your profile.
Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them