A contribution at a conference usually involves writing and submitting an abstract which is then reviewed and either accepted or rejected. If accepted, the content is usually assigned to either an oral or poster presentation. You then go to the conference and either talk in a session or stand by your poster and answer questions on it. Some conferences also have a book of proceedings or perhaps a special issue journal, which you can then write a paper for, based on your presentation at the conference. Needless to say, a conference is a very expensive means of getting a publication and this is not always guaranteed.
By contrast, a journal paper does not involve attending an event. You ‘simply’ write a paper, based on your target journal’s author guide, and submit it. This paper is then sent out to reviewers, who will read it and decide if it is worthy of publication in that journal. If accepted, you usually have a list of corrections to make and then you submit.
Given that a journal publication is peer reviewed it is considered a more valuable publication and is generally more difficult to get accepted.
Dr Linzi E. Amers-Dodd 