For automatic exposure lock, there's a button on the back of the camera. To lock the exposure, it is pressed once, to unlock it is pressed again. Nice and simple.
For manual exposure, the shutter wheel is moved from "A" to a shutter speed. In the left side of the viewfinder, the meter shows the shutter speed setting and if the meter indicates something different, the meter's preferred shutter speed flashes, otherwise only the current shutter speed is displayed.