Its really no big deal,although its been a while,what I did although its crude and there are probably better ways-is to take a 2x4 measure the string length on it and put in two finishing nails that distance apart(allowing a little roon for error to the longer side)and start wrapping my b50 around the two nails until I get the desired number of strands.Then wrap the serving close to the middle,wrap your loops,seal the servings with fingernail polish or glue or something,give it a couple twists,wax,check the length to your bow...Its not that complicated but my first few were really ugly because serving the loops is akward at first and its hard to know exactly how big to make the loops without another string to measure.
I have probably just given you enough info to get you into trouble,but hopefully when you start,it will start to make sense.
Good luck
Robert