That’s an interesting challenge. One hour at a podium talking to a sit-down audience with no visual aids (presumably indoors) is quite a bit different from the iNat tutorials I’ve done.
I would start by asking who the target audience is (general public, students/teachers, bioblitz participants, conference attendees…), what they expect from this presentation (entertainment, education, how-to instruction,…), and how much background knowledge they have. Do they already know what iNaturalist is and how it works, or is that the subject of the talk?
Another question would be what the expected format for this is. Your description indicates that the expectation would be you talking to an audience of listeners. If this is an educational setting, can you make it an active learning exercise? Do you know who is going to show up and can you communicate with the audience ahead of time? Or is this a “free to the public” type event where anyone can just walk in unprepared?
If I was asked to do an hour-long talk like this to a public walk-in audience where I have no idea whether they have even heard about iNat before, I would keep it more general and not even try to get into how-to details. I would maybe mention that there are video tutorials how to do stuff on the website and trust that those interested would seek those out to explore. My main focus would be on convincing them that iNaturalist is a great way to spend time and they should do it, too! The way to do this without visuals I think is by telling stories that the audience can relate to and take them sort of on a journey of how I discovered iNaturalist, how I’ve been using it, and how that has been of benefit both for me and others.
I would structure the talk following the general advice of 1) Tell them what you’re going to tell them (~3-5 minute intro), 2) tell them (body of the talk), 3) tell them what you just told them (~3-5 minute summary/conclusion), followed by leaving ~5-10 minutes for questions. That leaves ~45 minutes for the body of the talk. I would chunk that into three ~15 minute sections covering three key points/stories. (There’s a reason the three-act structure is a popular story arc.)
The reason to target ~15 minutes per chunk is the limits to human attention span. (There is a reason TED talks are limited to 18 minutes maximum.) After each chunk, I would try to have some sort of break, e.g. stop to ask for questions before moving to the next story, or take a moment of silence to pour a glass of water and take a sip. This signals to the audience that you’re moving on to another point and allows those who let their minds drift off to reengage with the next part of the presentation. (Even better if you can make your “2nd act” some sort of interactive exercise with audience participation.)
On the day of the talk, be prepared that without visual aids YOU will be the visual for the audience and dress accordingly. I like to wear my “milkweed village” T-shirt for talks about native plants, for example, so I can illustrate the points I’m trying to make by pointing out the plant-insect interactions show on my T-shirt. Having props to pass around would be great, e.g. bring your favorite field guides for identifying. Maybe make yourself notecards with keywords to jog your memory as a fail-safe just in case. Since you have a podium, you have a place to put them, as well as a watch so you can discreetly keep an eye on the time. (Nothing distracts an audience more than the presenter constantly checking their watch.) I don’t think you will need the microphone for this size audience but that might depend on the room.
Good luck!