Dumb questions that need no extra thread. Post them here.

I'll begin:

I was just looking around to find the crop factor of my sensor when I found mmcalc.com. Now, I knew that crop factor affects focal length, but this site also calculates the f-stop and says:

"Although your lens is “f/8.0” it will have the equivalent depth of field to an “f/12” lens. The amount of light your lens lets in will not change, only the depth of field or the “blurry part” of the image. "

I was calculating 35mm at f/8 and got 52.5 mm f/12

So what the fuck does that mean? Should I be shooting at f/5.6 to get an image as sharp as possible? Or is my lens still sharp at f/8 but will produce a deeper field and that's all?