An agents usually is an engineer licensed by the PTO to represent inventors before the Patent Office. Most patent agents are employees of industry, but some will take private clients. A few are in private practice to the public. Do not fall for the self-serving criticism the Attorney crowd lays against against agents. They are usually competent, experienced engineers and understand invention, design, manufacturing, and business practices.
Few attorneys do.
And the ol' ambulance chasers cannot represent a client at the PTO, but a patent agent can. Hiring an attorney to file a patent generally means hiring talent and privilege that you do not need to obtain a good patent. You also are hiring the hubris, fee and ethical structure, and other problems the attorney business has taken onto itself. Patent Bar study materials can be found at my patent bar exam page. That means use or do not use spaces, capital letters, commas, dots, etc unless they are a proper part of your Email address.