if you have the owners manual, check the index. I can't find mine right now, but I know that you have to hold the radio power button and another button on the stereo in for thirty seconds and then the on the stereo display - it will flash asking about resetting the tire pressure gauge. If you can't find your manual, repost and I will dig mine out.
Add brake fluid
(1) Have you checked he inflation pressure of the spare? (2) Have you re-set the warning system?
The light should extinguish itself after inflating the offending tire to the correct pressure. If it does not, you probably have a bad tire pressure sensor.
http://www.topix.com/forum/autos/chevrolet-impala/T4P2NGT979PJ7QT2P
disconnect your battery and then reconnect. The light should reset and turn off.
It is important to understand why the warning lights come on. The airbag light will come on in any car if there is an issue with any airbag in the car, an issue with the wiring to or from the air bags, an issue with the horn, or the wiring of the horn.
ADD FUEL
Evidently the oil level was low before you changed oil and was full thereafter.
Time to change your oil in your engine!
It's the tire pressure warning light.
Tire pressure warning light.
There is no separate warning indicator for the transmission on your Impala - the Service Engine Soon light will illuminate if there is a problem - you must have the codes read with a scan tool to retrieve them. By the way, what kind of problem are you having?