jobs are full-time or part-time, 1500-2500 USD equivalent a month depending on hours, in Spain no degree or TEFL certificate is federally required, although the TEFL certificate is highly recommended and worth the week or two it takes to become accredited.
teaching english is a great way to learn about the world, the attached link and screenshot lists the requirements for that job in Spain specifically: native english speaker, that's it.
the best qualification to get is a TEFL certificate, a lifetime accreditation that can be completed in a 1-2 week online course.
If you're interested in general teaching insights regarding TEFL opportunities, I'd suggest the FAQ or previous posts in this community, which explain costs, TEFL, teaching opportunities and available jobs, and if you have any specific questions feel free to ask away.