External hard drive-don't want to back up EVERYTHING

Okay, I purchased an external hard drive to be able to use it more like a flash drive. In the sense that I want to be able to back up my photography, but I don’t want to back up EVERYTHING on my computer. I would like to be able to just select folders and drag them to the external hard drive. Is this possible or can i only use it to back up everything? 

You can use drag and drop. Mac may have a Sync app also Windows does.