NST (Nonstress Test) Monday

Jax
I'm 31.4 and I have to start doing NST every week due to being high risk. I've never had one before so I don't really know what to expect. Can someone fill me in on the process of this test? What will I have to do ...and when will they start checking my cervix for dilation? Kinda nervous for Monday. Lmk. Thanks.