There are two ways that people who dabble in drawing become professionals in the career. The first is by building up a portfolio of work, and marketing themselves, usually to smaller publications and local ad agencies, and then building a network of contacts up from there. The second is by going to a formal education program centered on graphic design. The second way builds up impressive technical skills, and many artists mix both methods. While in school, many graphic design students work as interns or as contractors at small publishers.
Knowing the tools for graphic design and page layout is essential. The vast majority of art made today is digitally composed or painted, with the leading packages coming from Adobe Software, particularly Photoshop, Illustrator, InDesign and Dreamweaver. While there is some overlap between graphic design and web design, web design is a much more technical field, and is more akin to being a programmer who knows how to use a raster paint program than being a traditional media artist.
What are the traits needed to be a successful graphic designer? Reliability, reliability, and communications! The vast majority of companies that hire contract graphic designers hire freelancers, and most graphic designers starting out start as freelancers, trying to build their professional reputation and a solid network of satisfied clients. This means that time management (to tell a client how long a job will take), scheduling and self discipline (to do the project when nobody's breathing down your neck) and communications (to let a client know when a project is running late) are essential. Nobody can survive in the graphic design field if they lack an appreciation and deep respect for deadlines.
What does being a graphic designer pay? To be honest - not much! Most entry level professionals make less than 28,000 per year. The high paying graphic design positions are all 'post design' jobs, where the creative design talent has been moved into a managerial or other position, doing art approvals design logs and more.
Graphic designers don't generally get into the business for the paycheck; they hope they can make enough on the paycheck to stay in the business. This is similar to other creative professionals, and most graphic designers take the time to do other creative endeavors for self promotion, such as creating their own intellectual property that they market.