Valve "screws"
Most valves have a "bleed" scew. Open it by turning counter clockwise, and when pressurized, the valve will open, causing water to flow thru it downstream. This is a convient way to manually open the valve. After opening with this screw, you can close the valve by turning it clockwise.
The flow adjustment is usually a bigger "screw" which adjust the flow (somewhat) thru the valve when water is flowing thru it. Some use this as an adjustment once the zone is installed, such as in instances where misting occurs with sprayheads.
Jeff