Do I have to type su every time?

I have created a user. useradd -M -d /usr/my_user my_user chown -R my_user. /usr/my_user Now as a root I can type: su - my_user -c /usr/my_user/some_dir/script.sh but if I want to do more complicated things, for example navigate between **my_user** folders I have to type the su - my_user pattern every time. Otherwise it states that I do not have permissions. How can I make my life easier and not type the su every time?