You have several options. Spanish digital TV, via an aerial, gives you the option of changing to English if the original programme was in that language. They are not English channels, though but have quite a good choice of American series to choose from. This system is free as it just connects to the aerial socket in your wall.
A rebroadcaster. These are companies that pick up the channels on their big dish and than retransmit them to you via a small dish on your roof. The legality of these companies can be questionable and they will charge around €20 a month. There may be a setup fee of a few hundred euros. Many of these have gone out of business over the years and people have been left with no service after paying up front.
Internet provider. These companies offer broadband, telephone and TV. TV channels are English and can be limited in choice. Again, set up fees of around 1 to 2 hundred euros (some are offering free setup). Usually a monthly fee of around 20 to 30 euros. Some of the bigger companies (the real, legal one) can charge around 40 to 60 euros a month. Not all the bigger companies give English channels. You can access English channels on your PC for free but generally needs hiding your Spanish IP address as things like BBC iPlayer requires a UK address. The IP hiders generally have lots of advertising or will charge a few euros a month.
Cable companies. These connect you with a cable instead of a broadcast signal. More stable in periods of bad weather but more expensive to set up. Again, a monthly fee is required.
A dish on your roof. You can access free channels from the Sky satellites (or any satellite in range come to that). The size of the dish will depend on the area you are in and the installation costs can vary from 400 to 1200 euros or even more. The advantage is there are no monthly fee and, once set up, you get the English channels with no further payments except, maybe, a dish realignment every few years or so (depending on high winds etc or if the satellite changes). You will get the definitions of free to view, free to air, freesat, freeview etc etc but, suffice to say, you will get lots of channels with no extra charge or the need for a Sky card. If you have a Sky box with card, you can bring your card over with you on holidays etc and use it. Against the T&Cs for Sky but a couple of weeks a year won't really break Sky. Using the Sky card permanently means telling a fib as you need a UK address and is expensive. If you get a problem and need to contact Sky from a Spanish number or address they will terminate your contract.
Look in the free papers and TV papers. Loads of advertisers in there for TV suppliers.