The best documentation is from the source files themselves. When you create a project, these files become a part of it and you can view them as needed.
STM32CubeMX/STM32CubeIDE can generate initialization code to get you familiar with how to use things.
There is also this manual, but I think the source files are a better place to find information.
https://www.st.com/resource/en/user_manual/dm00122015-description-of-stm32f0-hal-and-lowlayer-drivers-stmicroelectronics.pdf
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