Firms and individuals should hire a public relations agency when they want to protect, enhance or build their reputations through the media. A good agency or PR practitioner can analyze the organization, find the positive messages and translate those messages into positive media stories
A lot of colleges have degrees specifically in public relations, sometimes referred to as strategic communication.
A day to day in this career is going to vary by the industry. But you're going to be working on messages to the public - this might be via social media or even planning/working events.
It's a great and growing field. A degree in communications qualifies for you many different positions!
Personally my degree is in public relations but I've worked with colleagues who have general communications degrees, journalism degrees, marketing degrees and even business degrees.
Hope that helps!
It really just depends what what type of industry you go into and if it's in an agency setting or not. You could be doing a lot of writing, or social media. You may be planning events for clients or doing a lot of community relations. Regardless, people thinking that they need to go into this industry need to be very detailed oriented, willing to role with the punches and flourish in an every-changing and extremely fast-paced environment.