Just thought of starting with something "cool" and LFS came
to mind.

So, since LFS is said to teach us the ins and outs of Linux,
I wish to know how do you actually remember what all commands
you have issued, what kind of 10 parameters they have, what
are the alternatives to them, and all?

Of course you'll say - repeatedly read the man pages till you
die. Well, I don't think that is actually feasible. It'll get
boring. LFS is a big book.

Also, I don't want to look like "copy pasting" commands from
the book to computer.

I want to remember the things in a practical way - Is there a
way out?

Is trying to remember all the commands a meaningless idea?
How should I start LFS so that I actually understand and remember
what the hell I am doing?

Is it all about the "commands", or is it about something else?
Am I missing a point?

In youth i was self learning basic language.. family got me on trip without any PC's nearby. English is not my native, so not to be bored i grabbed Cannon Navigator manual(or it was direct paper print of BASIC help?) with me, one notepad and a pencil. All trip i was writing commands list with Russian translation of it and possible practical use cases from head. Needless to say at end of trip i was pretty confident about BASIC commands.
In linux i keep ~/bin/ directory where i place scripts that i made/find usefull to do some non-trivial tasks,second usecase for them is cheatsheet of commands and their usage scenarios.
You can't remember all. But can find associative way to remember some,some of them is short names for exact actions. Made your own ~/bin/LFS_*.sh scripts with modifications and use them.

LFS is not learning which commands I have to use to build the system. LFS is learning what software makes a Linux system, how does it work together, how has it be to be configured. It is more about grasping the concepts than learning how exactly every screw that bolts up the system is built.
So, IMHO, it is pretty pointless to learn every command exactly. Just try to memorize what the commands intent to do and, first and foremost, why are they used, not how. For example, don't learn how to create a specific symlink, you can look that up in the manpage. Learn why it has to be there instead.

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Thanks very much. I was thinking that learning "commands" isn't going
to be much meaningful. Your post is enlightening.

Now when I prepare the notes, I would write "what" I did and "why",
and what would have happened if I didn't do "that".

I agree with what the others have said, but I wanted to add my opinion that copying and pasting is not a bad thing. You can teach yourself about sed syntax and so on along the way, but it's not necessary (or even useful) to memorize the commands that you have to enter to build an LFS or BLFS system. I would never want to hand type all of that stuff even if I had a photographic memory.

for me it is something like a language, the words of the "linux" language. They are not [only] commands, but I ask and "he" gives me an answer. So you need to learn a language to be able to speak in that world. You will learn the words you use frequently and will forget others. During the time you will learn what you need, you will be more familiar with it, you will have practice and experience and you will see the concept, the structure, the spirit of it.