My guide here explains Layer Masks (second page): [link]
You would use the Transparent Pixels Lock when you have a layer that contains transparent and opaque parts and you only want to change the opaque parts. For example, if you wanted to color different parts of your lineart different colors and only the lineart is opaque on that layer, you would turn on the lock and then use the Brush tool to color over the lines you want to change without affecting anything else.
Yes, only the lineart will change color (it doesn't have to be black). Anything that is transparent won't be affected. Just keep in mind that if there's something not completely transparent (say there's a spot you missed that's semi-transparent), it will also change color, so the lines must be the only thing opaque on the layer and everything else transparent to get the best results.
I suggest you look at my introduction to Photoshop tutorial here: [link] It just happens that I did it on CS5 so everything should look the same. I go over layers and the locks at one point (on the top right I think).
Didn't go over masked layers though. They're really easy though. There's quite a few different techniques as far as coloring with them, so I'll just give you the basics of how they work.
Once you mask a layer (by going to the small icons on the bottom of the layer panel, it's the square with a white circle inside) you'll have that layer than right next to it what looks like a white layer. You click on the one you want to "be" on. If the mask is white, the stuff on the regular part of the layer is seen. If it's black it's not. Note that adjustment layers automatically have masks added so you can easily only adjust parts of the image. Now, you might be wondering what the little link is between the two parts of the layer. If it's on, the mask moves with the pixels below it when using the move tools. If it's off (by clicking on the link it'll disappear) than you can move the mask around without affecting the pixels below it.
I'm not the best person to explain. As far as I know, normal masks you can use a brush, vector masks or the other one can use shapes and paths (I think) and quick masks, you turn it on, draw with red where you want to select (sort of like the want tool but with a brush), and you click the quick mask again and it selects that part of the image for you. You can then click the regular mask button and make a mask from your selection. You can make a mask from any selection btw, this is really handy.
I don't know much else. You're better off searching for a mask types tutorial or something.