Gem PATH Correction

I installed some additional gems for a project I am doing, and they show
up not in the Ruby System Library, but outside of it. Also, I get the
error message "gem executables will not run because (file) is not in the
PATH". How can I fix this and put my gems in the right place so that
they work?
Thanks to anyone who can help with this!

If you are on Ubuntu or similar did you forget to use sudo on the gem
install command? If so just do the install again (with sudo
obviously).

Colin