Abonos are ticket packages. You will usually see advertisements for them for transportation like trains or the metro; like a season pass for Six Flags or Disney. However, these are quite cheap for the amount of travel you can do with them. The price is a set amount of 20 euros.
I bought a “abono recurrente” for Salamanca to Principe Pio and it had unlimited trips. The pass was active from the time of purchase until the end of April. The pass is for getting back and forth. This meant I just had to make sure my train was going in the right direction before looking at the dates and times available to book it. However, if you have a plane to catch in a short amount of time it might not be the best option as you must transfer from Principe Pio to train line C-10 towards Chamartín then transfer again towards line C-1 to Terminal 4 of the airport. But if you have the time and are not carrying much luggage this is a very affordable option to get to the airport. You could also get an abono towards Chamartín station instead. The only difference is you would have to request that station when you buy your abono as the automatic station in the abonos for Salamanca is Principe Pio. It is also easy to cancel and change tickets without getting a refund or paying a difference like you would with a normal train ticket. I was able to change my train ticket from a departure at 9:44 A.M. to a departure time of 12:28 P.M. the day before my trip with no complications. As long as seats are available for the train you can book any time or date with the abono.
To buy an abono you must go to the Salamanca train station with your passport. A good tip to do beforehand is to make a Renfe account to have the pass on your phone and linked to that account. You may also be asked to create an account while there if you do not have one because the pass allows you to book the train tickets, but each trip will have a different ticket that will be scanned and validated. Once you are at the train station you must go into the Renfe area and get a ticket to wait your turn. Once it is your turn you go up to the ticket booth and ask for the abono. I will say you do not need much fluency as all you need to say is “Quiero comprar un abono a Madrid.” And as stated before you can ask what train station it stops at with the question “A que estacion termina en?” and possibly change which station you go to by saying “Quiero ir a (insert train station name)”. But if you feel more comfortable doing so you can go with someone more fluent or in a group you can.
It is very easy to buy and use and is an affordable alternative to buying a bus ticket to the airport every time and if you have enough time to make the transfers and walk. It is also beneficial if you plan to travel to Madrid repeatedly. And the Renfe employees are quite helpful if you have any questions or want more information.

Raine Botello
I am a Mexican, Queer, Posse scholar. I am very excited to study abroad and open to all the experience I will have. From good to bad, I am ready for the challenges that await and am ready to share my experiences.