The bridge and a small village of Ave, no services.
Turn right at the first fork after the bridge. Cross through town and back uphill to the N306, which has wound its way back from where you crossed it last.
Turn right on the N306, and then left on the first road. It is well marked with many arrows and a Camino de Santiago information board. If you happen to stay on the N306, you will find more arrows. It is dangerous and noisy, and you are advised to turn back.
The camino is clearly marked but anything but straight. Check the direction at every intersection and you will arrive in São Mamede without trouble.