Can't have a root access for modification

well I’m a bit confused why I can’t modify any files inside the home directory, for example modifying the list of repo…
in the 2 subjects below on the forum it seems that it is accessible and required in some cases…
if I want to learn more about how to use properly Linux, step by step I should look into it I guess

(wget http://repo.puri.sm/pureos/pool/main/p/pureos-archive-keyring/pureos-archive-keyring_2016.09_all.deb && dpkg -i pureos-archive-keyring_2016.09_all.debà ) → It doesnt work for me…

PS : do you have any advice regarding a book to start with to learn and easily going into Linux and Debian infrastructure, to understand the distros and who it is basically operating ?