Your pass is your ticket; you don't need to buy any other tickets. For France and Spain you will need some reservations though. Although in France you can also travel without reservations using regional trains (TER); It just takes longer. In Spain that is only possible on some routes (e.g. Portbou to Barcelona), because Spanish railways also have mandatory reservations on some regional trains and some routes don't have regional trains at all.

You can buy reservations for Spanish trains already in France, at the ticket office.

If you have a global pass, you can travel as much as you want with the participating companies, whether it's within a country or not.

Am I able to buy those seat reservations in a train station in Spain with my Eurail? I’m thinking of making a trip to Portugal from within Spain so would they take my Eurail pass? I’m asking because my friend has already made the trip and they said they were told they don’t use Eurail passes there.

Certainly.

I'm not sure why you friend would say that but Eurail is also valid in Portugal. Regular fares can be quite cheap though so a pass may not always be good value.

Ok so I've gotten more details from my friend. They were basically told they couldn't get a seat through Eurail and that it was expensive otherwise. What I interpreted from that was that they wouldn't accept seat reservation purchases with Eurail and had to pay full price for one. They were staying in Toledo. They are saying you can't get the discount for the Eurail in July. Could you fact check that for me? 

Who told them that ? A RENFE ticket counter ? There is no quota for passholders, whether they use Interrail or Eurail, so as long as the train is not full it shouldn't be a problem getting a seat.

Keep in mind that low-cost companies like Iryo, Ouigo or Avlo in Spain are not included.