The green arrows indicate where the lights go inside the taillight housing. To take them out of the housing, just put your hand around the base of the light, called the socket (you can see that the sockets for the taillights/stoplights in the above image are black, and the reverse/backup light socket is white or cream colored), and give the socket a good twist to the left or the right, but usually to the left. It should pop out without any problems. Once you've done that, you take the bulb out of the socket. Use a small towel or in my case a raggedy t shirt, and put it around the bulb and give it a good twist to the left. You might have to wiggle it while you're twisting a little bit, but eventually, you should feel it kinda pop. When that happens you just pull the bulb straight out of the socket.
Once I did that I consulted my Firebird's owner's manual to see what kind of bulbs the taillights are:
You'll notice that it says 1157 next to where it says Stop Light and Taillight. So I went to the Autozone right around the corner from my place, and found the aisle where they sold the bulbs. I found ones that said 1157 on them:
I bought these, which cost me less than five bucks. Now when you put in the new bulbs, notice the two little notches on the bulb:
You'll need to match up those two notches with two slots inside the socket.
So then you just put the bulb in the socket with the notches on the bulb matched up with the slots in the socket, and give it a twist to the right to kind of lock it in the slot. Once that's done, all you have to do put the socket back up into its hole in the taillight housing, and twist it left or right to lock it in place. A note about the owner's manual though...sometimes it won't be entirely accurate. I found out that even though my owner's manual said that backup bulbs were 1157, when I took the bulb out of the socket, it was actually an 1156 bulb, NOT an 1157 bulb:
So what's the difference between 1156 and 1157 bulbs? Well, if you notice in the above image, the 1156 is a single filament bulb, so it has one contact at the base of the bulb. The 1157 bulbs are dual filament, and they have two contacts at the base.