Mod posting is the act of using your staff account to make a modified post, which can do many things.
To make a mod post, first log in to the Manage Panel. On the menu, click 'Show Posting Password'. You will now see a string of text. Copy this.
Go to the board that you would like to mod post in. Once the page has loaded, the mod box will appear at the bottom of the post form.
Paste the password that you copied into the box. Change any options that you want to, and then post.
To add boards to the menu, you first have to make a section. If you haven't done this yet, do it now.
Go to board options. Select the board that you want. Scroll until you see Section. In the drop down box next to this, select the section that you want this board to appear under.
Save the changes. Reload the front page, and your board should now appear.