If you wanted to be displayed everytime you opened up your terminal, then put this line into the bottom part of your .bashrc (if you are using bash):
. /usr/bin/screenfetchNotice the dot in front and there's a space gap between the dot and the executable script. Test it by close your terminal and fire up another one.
You can try to have a look on other distro's logo by using -D parameter, for example:
screenfetch -D 'ArchLinux' screenfetch -D 'Mint' screenfetch -D 'Ubuntu'