Hi you get a leaflet from a participating bar/restaurant or the town hall sometimes have them.
The bars participating usually have a sign outside.
On the leaflet it tells you the name of all participating with what tapas is being offered also a map of the area and location of each place, the price is the same at all participating, a tapa and drink is include in the price wine/beer water etc. On the form you can nominate your favourite and possibly win a prize it is great fun going round especially if you go with a few friends you must try it.
In Beijofar they usually have a free train that goes round the rout picking up and dropping off at the various bars participating it's a great way to try places you have not been before just be prepared to enjoy