Your City Tech ID gives you access to campus via any of the turnstile entrances. It also serves as your library card at all CUNY libraries.
New hires should have received a form from AWMO (the Adjunct Workload Management Office) or OFSR (the Office of Faculty and Staff Relations) which you can take to Public Safety in Namm 112 to get your ID.
Please see this page from Public Safety, which includes hours of operation for the ID Center as well as information about what to do if you lose your ID or if your current ID isn’t working at the College turnstiles.