Rewinding the clock a few years back, I didn't use Dropbox all that often - even the 'cloud', I never used often. I relied mainly on my Google account, and my QNAP NAS. When I started here at TweakTown, I needed something where I could access all of my work, on any machine, on any operating system, anywhere.
I jumped into Dropbox when I purchased by Galaxy S III, as Samsung were handing out 50GB of free Dropbox storage - so I thought I'd use it. From there, I've uploaded tens of gigabytes of data to the cloud, and have it synced across multiple machines, operating systems, and even on my NAS.
Your first step, of course, is to ensure you have a Dropbox account - if not, you can sign up here.
I'm going to presume you're using Windows here, so once you're signed into your Dropbox and have some files synced, you'll have a 'Dropbox' folder in your Users directory. This folder, is the folder that everything is stored in, and you'll access this constantly.