Exporting resources in a jar file

From my understanding, a jar file is basically a zip file that’s compressed to run using each other.

How I load my resources

wood = TextureLoader.getTexture("PNG", ResourceLoader.getResourceAsStream("res/wood.png"));

I have a folder that’s not under the src folder, it’s its’ own foflder. example:

scr
packages

res
libs

I figured it out using this syntax, but forgot. Right now I have a jar file in a folder with the res folder. How can I make the jar file hold everything itself.(Such as minecraft and other downloadable java games) Whenever I export it cmd tells me it couldn’t find the textures.

exception:

Exception in thread "main" java.lang.RuntimeException: Resource not found: ./res
/FlubberFlap.png
        at org.newdawn.slick.util.ResourceLoader.getResourceAsStream(ResourceLoa
der.java:69)
        at com_FlubberSpace.Game.main(MainFS.java:87)

Can you also explain what happens when I put ./ and / before the res.