When you use the -makemod command a folder with the following files will be created:

project.xml
image.png
readme.txt
content/ 

You should place your mod files in the content folder.

Here is how you should configure the project:

<data>
	<title>Set title here</title>
	<description>Write the description here</description>
	<tags>tag1,tag2</tags>	Set you tags here separated by a comma.	
	<visibility value="Public"/>  Possible values are: Public, Private, FriendsOnly.
	<previewImage value="image.png"/>  You can change the image file here.
	<changeNote>Initial update</changeNote>
</data>

When uploading you agree to the Steam Workshop terms of service. See the following link:
http://steamcommunity.com/sharedfiles/workshoplegalagreement