By most European standards, Spain is a BIG country and at some stage you are going to have to get around it. Unlike many travel guides, I am not going to say,”It is easy and amazingly inexpensive to get from anywhere to everywhere”. Spain’s infrastructure varies between lamentable (public transport in rural areas and excessive (too many empty airports!). Let’s be more realistic
There is not a national fully-integrated long distance bus travel company. The nearest that Spain has is ALSA Coach Travel. I use them frequently and I find the services excellent, punctual and secure. What I do NOT like is their website. They have some excellent weekly/monthly tickets and other offers BUT there are often problems with their site or you have to go 50 kms to buy a ticket in person from their office for travel the next day! For example a one week pass for only 100 euros! The company is now owned by National Express and I hope improvements to their admin will be made. They do have excellent support in the English language ….. via Facebook!!
The national rail company is RENFE which covers the overwhelming majority of all rail journeys in Spain. Usually the services are fast, punctual and safe. Spain has one of the highest totals of high speed rail miles in the world. The challenge is that the route network is horribly thin and your journey may start a long way from any station. The RENFE site is in English but again be prepared for technical gremlins when booking. Prices vary from wallet sucking for immediate 1st class AVE (high speed) journeys to very reasonable, especially when they have special offers on.
Recently Trenes was launched to offer budget rail travel but sadly is not available in English yet. I would recommend keeping an eye on that site.
Some important links below and check the overviews on the left menu.
Map of Spain