The main bearings are located under the, aptly named, main bearing caps. There are 5 of them and they are the the part that holds the crankshaft to the engine block. They have 4 bolts apiece, two in the horizontal position and two vertical.
I highly recommend investing in a service manual for your car if you are going to be doing this sort of work. There are a LOT of torque values and sequences that must be followed to do the job correctly.