On your PC, right click on the folder, go to Dropbox and 'Share this Folder'... you can then enter email addresses. When these people sign up/log in to Dropbox, they'll see your folder. I think they'll get write access, too.
Alternatively, use the Photos folder as follows:
Dropbox photo galleries allow you to share photos with anyone (even non-Dropbox users). These photos will be presented in a photo gallery that is viewable online.
Step 1: Make a folder inside the Photos folder, and give it a name (this will be the name of your photo gallery)
Step 2: Put photos inside the folder you just created.