Office Administration covers a lot of areas; you'll also hear it called Business Administration. You could be the office manager for a small company and the only person that works in the office. Or you could work for a large company and be part of hundreds of people that work on the administrative needs for the business. Having an education and experience working in business administration provides tons of opportunities, as every single business needs someone to help keep it running by doing things like: ordering team lunches, paying the bills, fixing the copier when it's jammed, ordering office supplies, answering the phone, etc.
I recommend getting a job at a company before deciding that you want to go to school for Business, even if it's just part time. You'll know pretty quickly if you like it.
If you decide to go to school for Business, there are a variety of programs that will help you succeed in the workplace. You could take individual classes in things like Microsoft Excel and Microsoft Word; these would boost your skills immediately in any business. Other options include a Certificate program (usually 1 year), Associate's degree (usually 2 years), Bachelor's degree (an additional 2-3 years after finishing an Associate's degree), and an MBA (an extra 1-2 years after finishing a Bachelor's degree).
The most important advice I can give is to be curious -- ask about things that are interesting to you and follow that path. What's interesting to you may change many times in your life, but it doesn't matter as long as you're curious about what you're doing.