What can a id_rsa.pub file be used for?

What can the id_rsa.pub file be used for? I am working in machine A. I need to have an account in machine B. Another user from my team asked me for my id_rsa.pub (from machine A I suppose) so that he can create a user for me in machine B. Does this make sense? Is id_rsa.pub necessary for this? If so, what does it do?