Need to Learn about Databases

So, here's the thing. I have a Physics degree, and I am now (well, whenever coronavirus let us get out again) finishing my masters degree in Automation and Control. I've had Data Structures courses, but, due to some changes in the curriculum, I couldnt attend any databases course. So, I would like to invest my free time due to the quarantine, to learn about databases. But, I don't know what should I study, so I'd be grateful, if you could point me in the right direction (technologies, courses etc)

Thanks in advance :)

And keep safe people