If you just want to invite your colleague into your Organisation, see Add Teachers but if you would want to add them directly into your organisation AND a course at the same time, see Adding Teachers to a Course  where for either option you can send an invitation email to your colleague and it will take them through signing up for a Codio account and also added them into your Organisation (and Course if you take that option).

You can also add teachers into courses as a Read Only mode. These teachers will only have access to the courses in Teaching Mode and will not be able to add/edit/change any content of the course. It can be done at the Course level and the Organisation level.