I am not sure what your aim is with this post. Are you asking questions or you trying to teach newbies and want them to make research?
If you want to know more about Bitcoin and blockchain a link has been provided for you and also I would recommend these website/books for you.
https://github.com/bitcoinbook/bitcoinbookhttps://learnmeabitcoin.com/I know something about seed phrase 12 digits letters can it be of 8 or something else i think 16 so in add to 4 is the thing??
Seed phrases typically have 12 words but can also be 18 or 24 words. The length depends on the wallet and how secure you want it to be. More words means stronger security.