In short: Spain has free official training to improve your employability (SEPE and regional courses, and professional certificates with official validity), plus online platforms to add skills to your CV. The key is telling apart what counts as regulated training (valid for employment and for socioformativo arraigo) from what is only complementary.
1) Free official training (SEPE and regions) — the kind that "counts":
- Employment training courses: free for the student, for unemployed and employed people. Catalogue per region.
- Professional certificates (certificados de profesionalidad): an official accreditation of a qualification, valid across Spain and the EU (Europass Supplement). 3 levels (1-3), 200 to 1,200 hours, with a work-placement module. They count as regulated training.
- These certificates are one of the routes for socioformativo arraigo (see legalizacion/arraigo-tipos).
2) Online platforms (CV skills) — NOT regulated training:
- Platforms like Alison, Coursera or edX offer open courses (many free, with an optional paid certificate). They help you add skills and lines to your CV (technical languages, office software, marketing, IT…), but they are not equivalent to a degree or a professional certificate and do not count for socioformativo arraigo.
General requirements: ID (NIE/TIE); for many SEPE courses, being registered as a jobseeker. Check the course and your region.
Official source: SEPE — Employment training.
Informational only; the offer, requirements and deadlines vary by region — check the official source and a professional for your case.