Add a line to the end of your ~/.bashrc file with:

    . $HOME/.bash/j.sh

(Change that path to point to wherever j.sh is, though ~/.bash is probably a good place for it.)

Thanks so much! Makes sense

I think what is referred to is bash's source command: when you've modified your .bashrc and you want the changes to be reflected in your current shell process, you do

  source .bashrc

or, equivalently

  . .bashrc

which runs .bashrc in the current shell, as opposed to in a forked subshell as happens if you did ./.bashrc ; and hence the new functions/aliases/variable settings you've put in .bashrc are now available in the current shell (as opposed to only being visible in a forked subshell and disappearing when it exits).

Now it's clearer, thank you! :)