Recommended sites for self-studying

https://www.tutorialspoint.com/matlab/

It's a well-organized tutorial for beginners. You can also find a damn long quick guide. (Really? Long and quick?)

http://mathfreeon.com/

It provides an on-line IDE for matlab. There are limitations for guests and no-charge users such as size of storage and number of projects. Premium membership has less limitations. Simple codes can be tested on-line when a matlab installed PC is not available. You may already know octave and GNU octave which are similar to that. I've never used them, but I'll study how to use and write something I wish.

https://ece.uwaterloo.ca/~nnikvand/Coderep/gui%20examples/A4-Gui_tutorial.pdf

This provides tutorials for those who has never used matlab GUI. Very easy to follow, enough to train your GUI skills and make you an intermediate user. It was a website originally but it seems like it's gone and you can find a pdf version there. If the site is blocked, please write a comment and I can send you the pdf file.

Making a GUI requires more skills than it seems because you should hide everything in code-level behind and make users and PCs to communicate only via UI. So it's fun and hard. But you can find that almost all the softwares we use give us nothing more than just UI and manuals. Designing and developing a GUI will make you think as an end-user as well as a developer. So there's a saying for programmers, "What you make will be used only by idiots and weirdos." (If you don't agree, just remember this: Shit happens.) Your bright work can be brightened only when it's used by someone else, not yourself. In that sense, studying matlab GUI may be a good starting point to be a GUI design/developer. Why? 'Cause it's easy to learn. Just try and you'll know.

Any recommendations would be very appreciated.