An "open jaw" simply means that you are returning from a different airport.
EXAMPLE:
Roundtrip:
SFO-AMS
AMS-SFO
Open jaw:
SFO-AMS
BCN-SFO
The "open" part of the trip is AMS-BCN.
If you create a United MileagePlus account you will be able to see the availability of award flights. These will be priced in miles, rather than dollars, although there will be some fees to pay in addition to the miles.
DO NOT TRANSFER points from Chase to United (or anywhere else) until you have confirmed the availability of award seats for your specific dates. Airlines make a limited number of seats available for award redemptions. Just because there are seats available for sale (with money) does not mean there are award seats available.