How Do I Connect 00 AWG Wire to a 100A breaker?
Short answer - you don't. I'll echo what others have said - don't guess - find out what you have. Size and whether copper or Al. Find out if you can make splices in your panel per local code and (if allowed) splice down to the correct maximum size that the breaker will accept. Tester says it correctly - 4 wires needed -2 hots, a neutral and a ground, but the ground wire may be a size smaller than the required "hots". 
ALSO - once finished, will you have two separate services both feeding off the meter pan? It sorta reads that way. I do not believe you're allowed to "Piggy back" wires on the meter pan and in my locale there must be one main to turn off everything. So- one main panel to feed two sub-panels. Draw and post a diagram if you can take a picture of it. Indicate hots in red and black, neutral in white and ground in green. This is the level of detail you need to understand it, if you do this as a DIY. About a year ago, I took on a sub-panel and ran flex metal cable throughout a new shop. I researched the heck out of. It was not that hard to learn and obey all safety rules, whether or not you have code enforcement.