Also, the slow speed dial has a little lock thingy to prevent it turning - press that in before you rotate it. It rotates both ways, and doesn't lock at the other speeds (just has a detent), but will try to lock when you rotate it from one side to the other - you can sort of press the lock button with the side of a finger as you rotate.
When using the T setting for time exposure, you close the shutter by rotating the dial a smidge towards B.
When going back to higher speeds, reset the slow dial to its locked position.