1. To enter one's name on an official list or record. You should finish registering in all your classes tonight. If you put it off any longer, they may not be available for the next semester. The class is filling up, so you'll need to register for it soon if you want to attend.

2. To enter one's name into an official register in a particular city, state, country, etc. You'll need to register in Dublin within a week of arriving into Ireland, or you could face problems with immigration down the line. The class is filling up, so you'll need to register for it soon if you want to attend.

3. To enter someone's or one's own name and details into an official list or record. In this usage, a noun or pronoun is used between "register" and "in." My case worker is registering me in an online class to improve my computer skills. I've registered my daughter in a number of clubs and activities for the summer.

4. To enter someone's or one's own name and details into an official register in a particular city, state, country, etc. In this usage, a noun or pronoun is used between "register" and "in." He lives in Britain, but he registered his company in France. You'll need to register your vehicle in the new country when you arrive.