I want to understand about what is step into and step out in xdebug phpstorm, and what is the difference between them, and what should i use most in debugging with xdebug phpstorm.
This isn't really a Magento-related question but I am happy to answer it.
Step Into means that you will follow the code execution into the next function to fire.
Step Out is exactly the opposite. If you don't feel the need to go line by line through the function that you are currently exploring, it will execute the remainder of that code without stopping unless you have a breakpoint set somewhere.
I made a tutorials series on youtube about how to use xDebug & PhpStorm together.
There are 7 total videos in the series. PHPStorm / xDebug