what dotfile can do in the tails

when the user read thier section of the Persistent Storage he will see they explain about Dotfiles as a way to save configurtion of the apps can it save the log in in websites or it just save the prefecne of useing the app so how can I use dotfile feature if the dotefile feature can not used to save log in so please suggest for me a distro that is live os (which only run from flash and dont fromat my laptop ) and at the same time save my logs