When you are in training, you want to bid your schedule so your trips conflict with training dates. The company will buy your trips, you fly the training schedule but get paid the schedule you were able to bid for.

For example, if you have training 1-14 October and can bid a 12 day 75 hour trip, you want to try and bid that trip to touch your training from 1-14 October. Lets say under the hypothetical training schedule you get a trip that goes from 5-17 October. The company will buy your 5-17 October trip and pay you for it while you do whatever flying is required during training. You could then GS for double pay between 15 and 31 October, assuming your category is short manned and you don't exceed any FAA flight time limits.

EDIT: but if you are a new hire it works a little differently. The company still buys your trips, but you only get paid your monthly new hire salary until you are off OE.