Although it isn’t essential to include hills in a running program, I believe it is one of the 3 key elements of any balanced running program. (If your calves can’t cope with the load from hills, then it is best that you concentrate on developing aerobic strength through longer mid week runs.
Hills no matter how you run them, elevate your heart rate, develop muscular strength in your legs and help your running form.
The RK POD program has different types of hill sessions detailed into it, long/ steady, short/ easy, short/ steep and combo (combination).
I recommend that you start with short/ easy hill that are not steep. It is important to allow your muscles, tendons and ligaments time to develop and adjust as your aerobic system does.
As you grow stronger you can progress to steeper and longer hill sessions; and of course the length of time spent on hills will naturally increase.