"Robert11" wrote in message

When horizontal clapboards are installed, are they nailed (only) to the
studs ?

That is the best holding power.


Or, to the studs, and between also ?

Not needed


How do they know where the studs are if they are covered by the clapboards
immediately prior to the nailing ?

You mark the studs on the sheathing before the clapboard is started. Use a
level and a pencil or a chalk line.