Fundamentals of Graphic Design

I know you mean web design, but visual design involves fundamental principles that can be learned.

Here is a Coursera class that will teach you the visual basics that apply in all visual arts fields (so color, shape, patterns, etc.).

I think you can audit the class for free.. be sure to ignore the marketing messages pushing payment.

Fundamentals of Graphic Design, Coursera

What's a good course/online class/book about actual design? (not html/css, but actual color theory, layouts etc)

I know it's probably something you learn with experience but is there any class? I was thinking about doing the Fundamentals of Graphic Design class on coursera and possibly this design course on codeschool (if it's completely free, not really sure).

Has anyone of you done that? are they enough? what would you suggest me?

Some information about me, i'm have a background in computer science and now i'm studying human computer interaction, I would like to also be able to design/draw the UI so that i could make an entire app/product from start to finish.

Fundamentals of Graphic Design

Why don't you try this free course in graphic design? Watch some of the lectures and see if you could see yourself doing this. Then you can major in it if it works. You still have a lot of time to decide assuming you haven't been to college before, your first classes will probably be gen eds that apply to either degree so you can switch around

https://www.coursera.org/learn/fundamentals-of-graphic-design?specialization=graphic-design

Not sure what you searched on Coursera -- this course from Cal Arts looks right up your alley and is part of a larger specialization if you wanted to learn more

As I said, my background is really poor, and most of the stuff I do at work it's pretty simple, so anything related to graphic design foundamentals will be good... I'm still searching the web to see what I can find, I might start with this course

There's a Graphic Design Fundamentals course on Coursera for free that you can do over the course of several months, if you want to focus on the basics of actual visual composition, balance, colour, type, etc.

https://www.coursera.org/learn/fundamentals-of-graphic-design

I'm an untrained UX designer with 20 years' experience, but I still found it a useful insight into what you actually get taught at design school.

I don't know of one specific course, sorry. Look for "foundations" or "fundamentals" of graphic design. Maybe something like this will work:
https://www.coursera.org/learn/fundamentals-of-graphic-design

I have been looking for a course for beginners too. If you want to start with the fundamentals of graphic design, you can check this one - Fundamentals of Graphic Design

And if you just want to start with the basics of Illustrator and Photoshop, you can check this - Professional Graphic Design Course

I would suggest the book Thinking with Type by Ellen Lupton, it's a great primer to the topic. Also this online "book" Butterick's Practical Typography in ten minutes. And this primer on the basics of design (color, type, grid): Readymag Design Almanac. There's a good beginner course on Coursera as well, you can get a free trial.

Constantly study work that you admire and try to understand why you like it or what makes it good. Use sites like behance.net to browse and save work. I'd also follow blogs/sites like It's Nice That(general design news/trends), Brand New(explains brand redesigns), Fonts in Use, to see how designers talk about their work. Read about the history of different graphic design movements.

Most importantly, constantly be making work of your own, and get feedback, and try to improve. You don't need fancy software-- many use Illustrator, but graphic design is fundamentally about composition and creating a visual language. In the old days people worked with paper, pen, and paper cutouts and made amazing work that modern designers still try to emulate. Don't get caught up with the fancy flashy tools. Good luck!