It feels like going into a country without ang knowledge of the language. You can be there for years and never learn anything. But once you have a foundation then learning is possible.
I was garbage at public speaking until I had to teach an ed. law course in graduate school. Now I'm exceptional at it.
It also helps if it's a subject you're super knowledgeable about. That helps.
I joined the committee and I was my job to stand up and announce the next weeks events, I used to imagine putting on circus masters top hat to get over my nerves.
I ended up going to various conferences run on formal lines and speaking at those.
I have also gone to a large number of "political" conferences run on formal lines (think roberts rules) both as delegates and standing order committees - which organize the formalities of business.
I was on may way to a meeting and bumped into John Bercow on his way to the house of commons, unfortunately I did not have my copy of Citrine other wise id have asked him to sign it.
Simon Lancaster has a good book on a mechanics of rhetoric and speech writing
https://www.amazon.co.uk/Simon-Lancaster/e/B005NAQX8U/ref=dp...
If you're in a reasonably sized city, there are probably dozens of tech meetups looking for content. Just start hanging out and you'll start seeing opportunities to talk. Take them.
Also, when you're just starting out, stick to topics you know inside out. Only write enough notes to remind yourself of what you want to talk about. And then just talk to everyone. Don't make it a "presentation". Too much detail and you might get worried about sticking to the material. Just wing it.