If you like the simple approach for software and are using a PC you can make a simple batch file in notepad or similar. Just type commands in and save as a .bat file. Simple but effective.
xcopy "path to files to be copied" "destination to be copied to" /s /d /h /y /i (/s is for all sub directories, /d is to check for date and time, /h is for hidden files, /y is yes to all when it asks to overwrite, /i create the directory if it doesn't exist)
This way you can just copy new or updated files to your external hard drive by executing the file. You can add a delete line if you use a directory like desktop as a temp place too so deleted files don't build up and more.
eg:
del "e:\backup\mypc\temp" /s /q
xcopy "C:\mypc\temp" "e:\backup\mypc\temp" /s /d /h /y /i
xcopy "C:\mypc\mypics" "e:\backup\mypc\mypics" /s /d /h /y /i
You can add as many lines as you like, works over networks too.