of thinking that you can "wing it" through a presentation.

For the purpose of this answer, I am assuming that an essay is written down on paper, and a presentation is given live by a person in front of an audience. I need to specify that because I don't want somebody thinking that this answer is going to compare a PowerPoint or Google Slides presentation to an essay.

A key difference has already been stated. A presentation is done in front of an audience. That audience might be classroom peers, a group of board members, or an audience at a conference. A presentation is given verbally; therefore, it presents information in an auditory format. A presentation will also convey information visually as well. This is completely unavoidable because things like kinesics, eye contact, platform movement, and gestures are all being taken in and analyzed by an audience. Non-verbal communication is key in a presentation. If the information is brilliant and earth-shattering, but the presenter looks bored and is dressed like a vagrant, the presentation may not be well received. All of those non-verbals are critical to a presentation. Word choice, organization, and transitions are also critical.

In an essay, most of the focus is on the organization, diction, and flow of the words on the page. Formal writing grammar is now very important, though it need not be advanced. Tone is also important in an essay, but it is much harder to implement because it must be done through the writer's word choice. In a presentation, tone can be conveyed through word choice, volume, gestures, eye contact, and other things.

Finally, a few similarities. Both formats are designed to convey information. Both formats can be very effective, and both formats can be incredibly difficult to master.

A presentation usually has visual aids.  A speech is more reliant on the spoken word.  When you give a speech, you are talking to your audience and they are listening. When you give a presentation, your audience is usually learning something from you and you want them to take some kind of action.

A speech is an event where a speaker stands before a group of listeners and transmits information by no other means than speaking to the group. The audience listens passively and may or may not be invited to ask questions at the conclusion of the speech.

A presentation may or may not include a speech. During a presentation, the speaker uses additional media to transmit information to the audience. These media may include visual aids such as PowerPoint or handouts, video clips, audio clips, and other items. The presentation may or may not include audience participation, and questions may occur during or following the presentation..

The main differences really boils down to the connotations of the words themselves. Speech is defined by Merriam-Webster as "something that is spoken,a usually public discourse."A speech is a type of oral recitation, whether from memory or notes. It is a way to communicate ideas auditorily to an audience, with a specific purpose in mind.

Presentation, on the other hand, is usually refered to as a more interactive experience. Salesmen present their sales pitch, showing the item being sold, demonstrating its good qualities, and letting the consumer ask questions. Presentations are about giving the information in a way that appeals to the audience, rather than necessarily speaking the information.