First off you should check your cervix at the same time everyday, preferably in the middle of the day because sometimes when you get out of bed in the morning, it will be high from where you've been laying all night and leads to confusing results.
Telling if it is high or low depends upon how many knuckles of your finger fit in there. If you can only put the first knuckle in, the one right below your fingernail, then it is low. If the second can go in then it is medium. If it is almost down to where your finger connects to your hand, then it is high. Mine is a little difficult to tell because I have a tilted uterus so mine is constantly changing and will even be different at various hours of the day.
Soft and firm is fairly simple. If you can wiggle it, I guess is the only way to say it, then it is soft. It is movable. If it feels like an unripe fruit and doesn't give much when you try to move it, that is what it feels like when it is hard.
Finally open and closed is another tricky one for me, because I've already had two vaginal births and 2 D&Cs so my cervix feels a bit weird all the time. Anyways, when it is open, you should feel a dip and you will be able to fit the tip of your finger in it. When it is closed, it will feel tightly shut, like pursed lips. There will be no indent.
Hope this helps a bit! Sorry for the tmi...