Someone please help me understand my car audio system. I'm new.?

ok honestly in todays market you can pretty much take the listed wattages they list on amps and throw them out the window. There is no rules or limitations to how they test so each company tests them differently. Now what is true is that when you half the ohm load of an amp you are effectively doubling it's power output which is a good thing as long as the amplifier will handle the load. I can give you the best way to hook up your amp with a suggestion for future upgrades.

take the front rcas of your radio and run them to the inputs for channel 1&2. These two channels will run your interior speakers at 2ohm stereo. The Front right + and rear right + go on the positive terminal of channel 1 the front right - and rear right - go to the negative terminal of channel 1. Repeat this for the left side front and rear hooking them to channel 2.

Now if the deck or radio you are using has subwoofer control run your rcas from channel 3&4 to the subwoofer output of the radio. If it doesnt have sub control use the rear channel output. When you bridge an amp you are really putting the same kind of strain as you are droppign the ohm so an amp that is 2 ohm stereo stable may not be 2 ohm mono stable (your owners manual will tell you but knowing sony it is probably 2 ohm stereo and 4 ohms mono stable)
So you should have either one 4 ohm subwoofer or two 8 ohm subwoofers so you can reach a final impedance of 4 ohms. (if you have two 8 ohms subwoofers you combine their positive leads together and negative leads together like you did the front speakers and this will drop the load to 4 ohms)
Now consult your owners manual for bridging an amp but generally 3&4 will be used and you hook your positive lead from your subwoofer(s) to the left channel positive and the negative lead from your sub(s) to the right channel negative. This will set your amp up for running the interior speakers on channels 1&2 @ 2 ohms stereo and the subwoofer on channels 3&4 @ 4 ohms mono. When you are ready to upgrade buy a monoblock or subwoofer amplifier and use that to power your subs and move the rear speakers connected individually and normally to channels 3&4 for a nice two amp system.

Ignore wattage handling and outout claims of products and just buy decent brand name stuff. You can effectively double the power handling of a speaker when you use a good crossover on it. When you are tuning in your system unplug the sub and tune the interiors first. Then plug in the sub and balance it out to the system. having the sub playing when tuning the interiors can cover up some distortion that can possibly harm your speakers.

have fun