A single person uses has. Groups use have.
- The committee has agreed to spend 100,000 euros to repair the swimming pool.
(Here we use has because in this situation we think of the committee as one body that agreed something.)
- The committee have gone on holiday.
(Here we use have because in this situation we think of the committee as separate people going on separate holidays.)
- Ten euros is enough to take today.
(We don’t think of the euros as money to count like 1, 2, 3, etc, but we think of it as one total – ten.)
Some sentences can have both plural and singular elements. Better to connect the verb with the nearest subject.
- Neither the desk nor the books have arrived.
(Books is plural so have.)
- Neither the books nor the desk has arrived.
(Desk is singular so has.)