Sooooo... (Ignores all the controversy)
Here's how FTM focus works. Put the camera in aperture priority mode (Av). Spin it down to f/4.0 with that new lens of yours. Zoom to 105mm for a nice, narrow depth of field. Someplace with some good light, find a relatively close object with some depth to it like a sideways shot of your keyboard, IIRC you'll need to be about 12" to 14" away with that lens. Press the shutter halfway down and the camera will autofocus, probably on that center + in the viewfinder. Still holding the shutter halfway down, play with the focus ring and you'll see that you can override the point that autofocus selected, moving it a bit farther back or closer. To get a bit better feel for this, use the depth-of-field preview button to see what the picture is really going to look like with your actual aperture.