Easiest steps to start is buy a recent (nucleo) F4 discovery board, it has the STLink debugger built in.
Join the STM32 community forum so you can read what others already stepped in to (their problems could be your problems).
Download CubeMX read how it works, select first only one or two peripherals to get started and generate the startup code.
Run this code in the SW4STM32 IDE environment , compile and run.
Oh yeah download the datasheets of the processor on the nucleo board, family reference manual, and other relevant documentation from st and start reading what you need.
Depending on previous experience this could be done in less than 1 day upto 2 days and you should have a blinky and simple uart working.