IEEE Repository has various types of documents including transactions, magazines, conferences and journals. What is the difference between the above four?
IEEE Transactions and Journals publish essentially the same thing: peer-reviewed papers, some shorter (e.g., briefs), some longer.
IEEE Magazine articles are most often written at a less technical level than Transaction and Journal papers (though, there are exceptions).
Conference papers are those presented at various IEEE-sponsored conference venues, and published as part of the conference proceedings.