You cannot actually understand everything at once, so it is normal to still be confuse, as you get accustomed with the forum you will understand both officiall and unofficial rules.
Is this forum strictly against plagiarism? then what if I quote a part of another website's sentence as a reference argument in the discussion? is it a violation?
Plagiarism is the most frowned act upon not only on the forum. You can actually quote anything to either add to the point you making but be sure to add the right reference that leads to that article. Not adding any reference link makes the enter statement yours.
Yes I've found that thread, I've read it but still confused by some terms, like multi sign
Un_rank has already explained the meaning of multi sig for you. Multi is just adding another security layer to your wallet where you have multiple keys and with at least two co signers before a transaction can be initiated. The most common multi sig are the 2-3 multi sig and the 3-5 multi sig, the higher the signatures the better the security. This kind of wallet can be set up when two or more people decide to hold their funds in a single wallet. This will protect one party from withdrawing funds without the other party(s) getting informed.
I would advice that once you don’t understand something you can just search upon it on the forum and if you don’t find any then you can create a thread asking the questions