Tolls?

Only on multilane motorways, similar to American interstate highways. Although many multilane freeways are free.
Prices vary depending on segments or even time of day (peak). Some freeways are only about 5 or 6 eurocent per km on average. Others have stiffer prices, even close to 20 eurocent per km. If there are tunnels, even more. Overall I never considered tolls a major part of the travel budget in Spain. At the end of the day, you are likely to spend more on hotel for one single night than on tolls on your entire vacation. So don’t worry and be happy. You save a lot of time with toll roads, but if you are not in a hurry, there are plenty of free, albeit slower, roads.

The way you pay is:
before you enter the freeway on the ramp you go through a toll booth. Pick up a ticket like you would do at any parking lot. Keep the ticket with you. When you exit the freeway, on the exit ramp, you will go through another booth. I always use the manual cash (efectivo) booth. Those booths accept cash and are attended. Give the ticket to the attendant, the attendant enters in the computer and the display shows how much money you owe. Give the money to the attendant and proceed.
Some booths may be unattended. In that case insert the ticket in the machine (like any parking machine in America). The machine displays how much you owe. Insert euro bills and/or coins in the appropriate slot. The machine gives change. But if you want the attendant just go to the booth that says MANUAL.
You can use credit card automatic toll booths, but I never bother. Even in my longer segments I rarely had to pay more than 15€ And I think the manual attended booths take cards too if you want.
There are also remote transponders, called Via T Telepeaje, but those are really for residents because you need to set up the autopayments with a bank account.

Drove the toll roads in the southwest of the country a lot in October and what you'll find is the large inter-city highways are tolled but the older roads aren't. So if you're driving and suddenly everyone is getting off chances are that's the last exit before toll and the majority of people are taking the free option. In those cases you are charged for the distance between the 'last exit' and the toll - if you exit off before the main road toll booth you'll pay a lesser toll for the shorter distance when you exit.

The tolls are usually a couple of euros. I think the most I paid was driving Malaga to Estepona on the AP-7 which is a solid hour and a half of driving for maybe 13 euros in 3 and 4 euro chunks for each section. The amounts were almost always odd like 2.45 or 4.60 and clearly based on distance. You could take the A-7 and N-340 and not pay tolls but the new fast, god condition road at lack of traffic make it well worth it.

The only thing you really need to know is whether you have cash or need to use a card because you need to be in the right lane so pay attention to the signage - they show cards and/or coins it's really straightforward. I seem to remember sometimes the 'pay with card' are little islands before the lines with the booth attendant. Maybe that was for people who couldn't use the tollbooth or needed to get out or something. I don't know what happens if you get in the cash line with no cash but it's not going to be pretty with a line of cars behind you.

If you use Google maps it will tell you if the route you've plotted has tolls and help you route around them if you can, but I would just be sure you have some cash on you because they are worth paying for.

Have a great trip!
=Tod

A slight expansion on what’s already been said. Toll roads will generally have AP at the beginning of the road number. In some places there will be a non-toll road, e.g., A6, that will have a section where there is a toll, e.g., AP6, then go back to non-toll. If you want to avoid toll roads, there are generally the old N (Nacional) roads that parallel most of the newer autovias. The road conditions are fine, but you go through the towns and will get stuck behind trucks, tractors, etc., thereby taking longer to get to your destination.