Step One)
Go to 'C Drive', then open 'Program Files'.

Step Two)
Open 'Steam'.

Step Three)
Open 'Steam Apps'.

Step Four)
Open 'Common'.

Step Five)
Open 'Age of Mythology'.

Step Six)
Open 'Mods'.

Step Seven)
Create a folder named after your mod. (Ignore the text file)

Step Eight)
Place any files related to your mod into the folder you created. (Ignore the text file)
E.g: An .scx file for a map.
It is recommended you add a .jpg called 'Workshop-Preview-Icon' that is .jpeg

Step Nine)
Launch Age of Mythology and click on the Steam logo.

Step Ten)
1 Select the mod you wish to publish
2 Select Publish

If you're already a contributer, ignore this part.
If this is your first time publishing to Workshop, Steam will have you accept their terms ingame.