Business cards help you maintain contact with the people you met at all types of events, such as recruiting or networking events. They should reflect your professional project and provide your contact information so employers can reach you.
Ideally, at the end of a conversation you've had with the representative of a company you are interested in or with a potential business partner!
You can also exchange contact information with your smartphones. But make sure to keep a business card on hand. The other person might prefer to have one, and everyone has cell phone battery issues from time to time!
It is very likely that the other person will visit your LinkedIn profile. Make sure it is up to date. Visit the page Create your LinkedIn profile.