Which way should the bed point?
In Eight Mansions feng shui, the rule for a bed is that the top of your head should point towards one of your four favorable directions while you sleep. Put simply, the headboard wall should be in a good direction from the bed. Tian Yi (health) and Yan Nian (relationships) are the usual first choices for a bedroom; Fu Wei (stability) suits anyone who sleeps badly.
That's a different rule from the bedroom's position in the house, which the Eight Mansions floor plan covers.
Which way should I face at my desk?
For a desk the rule is about the direction you face while sitting — your eyes, not the back of your head. Sheng Qi, the best direction, is the traditional choice for work and study. Note that the arrow on the desk icon points away from the chair: that's the direction you look.
The command position
Separately from compass directions, almost every school agrees on the command position: from the bed or desk you should be able to see the door without being directly in line with it, with a solid wall behind you. When the best compass direction and the command position conflict, many practitioners give the command position priority for the bed and the compass direction priority for the desk.
Couples in different groups
If one partner is East group (Kua 1, 3, 4, 9) and the other West group (2, 6, 7, 8), no direction is favorable for both. Common compromises are to use the direction that's best for the partner who needs more support at the time, or to choose a direction that is only mildly unfavorable (Huo Hai) for one person while good for the other.
Questions
My headboard is under a window. Does that matter?
A solid wall behind the head is traditionally preferred. If the best direction puts your head under a window, a solid headboard and heavy curtains are the usual compromise.
Do I need my house facing for this?
No — only north on the plan. If your plan doesn't show north, measure the facing with the facing finder and turn the arrow to match.