Both are means of delivering information, thus tools for 'learning'. Both can be delivered by one or more speakers, and are derivatives of lecturing, and often boring. A narrow topic presentation is usually fact-filled and as such contains the ‘meat’ of the topic sandwich. Al Gore is an example through his presentation of “Climate Change”, which is often excerpted within green technology seminars and conferences.
The hierarchy of oral delivery of information can be described as discussion groups (moderator, open floor or table discussions), presentations (narrow topic, usually single expert speaker, audience participation usually reserved to the end), lectures (single expert speaker, Q&A at the end), seminar (wider topic, one or more expert speakers, audience participation throughout the seminar), and conference (widest topic, containing multiple discussion groups, presentations, lectures, and seminars, often concurrently).
None of these terms have precise definitions, and vary considerably by context. For example, a seminar has a different meaning in the professional trades and academia, and even from one university to another. Presentations are even less well defined because they can be used to inform, as described above, or to persuade as in a sales presentation, or to influence, as in a political candidate’s presentation of views.