After having published a paper, am I still free to use & distribute it as I wish?
In most cases, journals ask for transfer of your copyright to the publisher. In these cases, you cannot technically distribute copies of the article any more without the publisher's consent.

The details of what you can and cannot do, however, differ between publishers. You will get a form upon acceptance of your paper that lists the legal details and that the publisher requires you to sign before they publish the article.