You've probably read some of the postings recommending that you really ought to get a good teacher if you want learn how to bow, even passably well. I won't rehash the debate except to re-iterate that I've played both the URB and the Bass Guitar and will tell you without hesitation that the upright is much less intuitive, especially when it comes to using the bow. Always remember to loosen your bow when your not using it. Pulling them out will only make the other ones loose.
People spend literally years learning and developing a really effective bow grip.
There's pictures in some of the method books - like Simandl. Basically, think of holding a softball, underhand. Then place the back end of the frog into the palm of your hand and let the upper part of your first and second fingers support the stick. Rest your thumb on top of the stick. Your control is going to come from the thumb and first two fingers - keep them curved slightly outward for strength and control.