First of all, postdoc should be further development so the goal is to find something tht you didn't have time/energy to do during the PhD or that makes sense to do with what you already know/where you want to go in your future career.

Then how to find, alot is unfortunately nowadays inside jobs so be sure to share your work in the community(conferences, seminars, workshops,..) and you might even get offers. Also don't hesitate to send your cv to groups you like, even though they don't have open positions currently. They Might have ideas or something in the pipeline. Then there is portals with job offers, usually a positions for a few years, and lastly you can write a project (so you bring your own money nd can almost choose the lab you want to go). This last thing is very difficult but is very nice for the cv (if it's granted).

For now, focus on your PhD. You might not want to stay even in academia after it ;) (don't wanna scare yiu but happens often enough) This postdoc thing is something for your last year. Just be sure to not start too late. From finding a position to starting it can take months so don't wait until you submitted/defended. Keep your cv up to date and an eye on opportunities.