Google Digital Garage
Google is among the top sources for free digital marketing resources, which should come as no surprise.
A nice place for beginners to start is the Google Digital Garage. The courses cover all facets of digital marketing in depth.
There are more than 30 courses, and two of them offer certificates of completion. These two categories are:
Basics of Digital Marketing
Educate yourself for the G Suite Certification Exam.
For product-specific courses and certificates, you may also browse the Google Skill Shop. These are more sophisticated and make a good addition to a CV.