What is the best way to learn all the illustrator tools and commands (for a beginner) ?
I highly recommend Adobe Tutorials, this is the quickest and easiest way I've found to get started with any of Adobe tools.
If you really want a reference for everything within Illustrator the most complete and accurate source is the Adobe Illustrator Classroom in a Book from PeachPit Press.
This is the "missing manual" that Adobe no longer provides. (PeachPit is Adobe's press house basically) It's dry, boring and tedious.. because it's a user manual essentially. But it will cover absolutely everything.
Proficiency with the tools/features.. merely takes practice.
You can not; you dont want to. It may seem like a good goal but it is not. Let me explain.
Many of the tools in illustrator and software in general are emergent. Emergent means that you can not predict the outcomes of the rules beforehand. Likewise you can not predict the usefullness of a tool by knowing what it does. A lot of the really useful uses for many of the tools is a entirely unintentional side effect of how they react to other tools and workflows.
So even if I could i couldnt enumerate all uses for illustrators tools. Nor would i want to as its not useful. And to be honest i dont know all of them, mainly because i can not remember all of the illustrator api, programing suites, postscript, svg and pdf references.
You can however get a list of all of them easily. Its just not terribly good to read it. But in reality you should skimread (not read) adobes documentation cover to cover to understand how to start solving problems.
Instead focus on what you want to do.
Learn on this forum.
Read every question tagged Adobe Illustrator, starting with the most popular ones right here:
Just reading what members are asking and answering can provide alot of in-depth knowledge.
Following this 'most voted questions' logic you're likely to quickly understand what are the most useful features, solutions, techniques, etc.
Start from these essential, 'most discussed' topics and then figure out if you really need to know everything.
To get started, you need a brief overview of all tools & commands available to you. Any short video off YouTube or tutorial blogs and good enough for that.
For in-depth, you could go through official tutorials & options or there are even lots of blogs online sharing tips for that, BUT I wouldn't recommend that for a beginner. The first step is always to actually "get started".
I highly recommend Linkedin Learning - they have courses in all areas but you can sort by industry and software. https://www.linkedin.com/learning/topics/graphic-design?software=Illustrator