postmarketOS is for Linux enthusiasts. For hackers, tinkerers, technical people who are interested in pushing their mobile devices beyond what can be done with the stock operating system: more free software, mainline kernel, getting software updates until the hardware breaks, better privacy, less distracting features, etc.
The goal is to make postmarketOS usable for non-technical people too, but we are not there yet. Usability and most importantly stability issues need to be worked out first. If you are looking for an OS that is as usable as iOS or Android, this project is currently not for you. You will have the best experience with postmarketOS after taking time to familiarize yourself with how it works, making it your own and contributing to development and/or testing.
What can be done with postmarketOS also depends on the device you are running it on. If you are just getting into Linux on Mobile, consider getting a second-hand SDM845 or MSM8916 device.
When compared to Android or iOS, postmarketOS is run by a tiny community of developers who work on the project in their free time - typically next to a dayjob, school or university. Keep that in mind when asking for help in the issues or chat. This is not a product you paid for and you don't have a support contract with us. People may help you if they have time, but sometimes nobody can help you and you need to figure out problems on your own. Be nice to everybody, follow the Code of Conduct.
Long term we plan to improve stability by doing a lot more automated testing (i.e. having phones in a test farm and continuously testing new software on them). In the meantime, users like you can contribute to improving stability by joining the testing team.
You will then get notifications when there is a brand new kernel or other improvements to test out, and can tell us whether everything worked fine or if you found a regression on your particular device.