Hello Damilola,
Public relations is about managing relationships with stakeholders including; employees, media, consumers, shareholders/ investors, the government, the community etc. So, media relations is the function under public relations which manages the relationship with the media — journalists, broadcasters, bloggers and influencers.
Registering with the NIJ means you want to become a journalist. However, if you are looking to build a career in PR, what you need is to register with the NIPR. Be sure to start at the entry level as you do not have any prior communication experience or qualification.
As for the skills required — you will be communicating with different groups, writing for an internal audience is different from writing for an external audience, the language and tone will also differ according to the industry. You must be a strategic thinker. It is important to know when to be quiet, when to respond and how to respond. PR also involves a lot planning. It takes careful planning to stay in the news all-year round so you will need to learn how to develop a content strategy for both traditional and digital media. And yes, digital is a must for any modern PR practitioner.