Using files in META-INF

I can put a file into the META-INF folder easily (just change the type to ZIP and then move it there) but how should I do to load the file in the program?
I’m fairly inexperienced with loading files and don’t even know how to load something from a folder lying at the same place as the JAR file, is there a difference to this compared to loading something from the META-INF?
If possible I’d like to be able to put folders in the META-INF folder and then load files from those folders (it’d make file handling a bit easier for me)