This website has a lot of resources. To keep you from be overwhelmed by everything, this page aims to simplify them and highlight some of the most accessible for beginning podficcers
A good guide to get you started is A Newbie's Guide to Podficcing by Azdaema.
I also have a less quick version of this guide on AO3 or available as a PDF.
If that isn't what you are looking for, I've included some more resources below ordered in what I think is the normal steps for creating a podfic.
Azdaema has a good break down on the factors to consider when choosing your first project here.
Something else to consider though is whether you have permission to record your chosen podfic. AO3's new ToS specifically mentions podfic under their II.D. Copyright Infringement section. In short, AO3 considers podfic to be derivative and not transformative. Because of this, you must have permission to post a podfic of someone else's work.
Now, you can always ask someone for permission. Please remember to be respectful and not badger authors though. No one wants podficcers to have a bad rep.
Another option is to find an author who has a Blanket Permission Statement (BP). This is a statement, usually located on the author's profile page, that tells others exactly what they can and can't do with their fanfics. Note, some authors do have blanket no podfic policies.
There is also a "Podfic Welcome" tag on AO3. This tag is for fanfic authors who would love a podfic to be made of their work.
First, you'll need a mic. There is no need to go out and buy a fancy one. Most podficcers start out using their phone or a headset mic that they already have.
Want to record on your phone? Check out #(no mic no editing software no idea) by reena-jenkins.
If you decide you love podficcing and want to invest in a better mic, most podficcers use microphones made by Blue (which is a Logitech brand). Of course, there a ton of other options out their though. Podficcing is about having fun and there is no one way to do it. Pick whichever option works for you.
Once you have your microphone, you'll need a recording program. Most podficcers use Audacity because it is free and easy to use and there is a nice setup tutorial here. If you'd like to try a different program, there are some other options here.
If you are happy with what you recorded, you are more than welcome to move on to the audio hosting & posting step. Some podficcers record and post without editing. Others do minimal editing to take out the mistakes/retakes/etc and then post. Still others take editing to the extreme and go above and beyond adding music, SFx and doing there best to make the recording sound as professional as possible. Again, there is no right or wrong way to do, or not do, this. Podficcing is about having fun, so you do whatever makes you happiest.
If you do want to edit your recording, I suggest you check out Editing 101.
For adding music or SFx, maybe start with this tutorial on multitracking to layer audio. And here are some sources for music and SFx.
AO3 does not have multimedia file hosting. This means you'll need to use an external file hosting website. The most popular and easiest to use options are The Internet Archive and The Audiofic Archive.
A breakdown of audio hosting options (and how to use them on AO3)
When it comes time to actually post your podfic on AO3, Shmaylor has a great guide, or there are more resources here. I recommend using the Podfic Posting Helper extension in order to make this process faster and less tedious.
Some people like to add cover art to there podfics. These are typically square images reminiscent of old CD covers. This step is entirely optional. It is completely valid to post your work without cover art. You could also post it using the "Cover Art Welcome" tag on AO3 and someone else might just come along and make some cover art for you.
AO3 workskins change the layout of your podfic for everyone who opens your podfic on AO3, unless the click the "Hide Creator's Style" button at the top of the page. These are how podficcers get their podfics and cover art to go side-by-side or in any other fancy layout.
Like with cover art, workskins are entirely optional. You can go without one, use someone else's, or make you own. All choices are equally valid.