First, in the zip file we're providing, there are two files: one is a .workflow file which is ripe for opening and editing in Automator, and the other is a .app saved from the workflow, which you can simply drag and drop onto Automator in the dock to open and edit as well (I just wanted to cover all the bases). No matter which file you open for editing, you'll see there are three actions that make Mail Man tick. The only one you need to really care about is the second action, 'New Mail Message,' and there are a couple of ways you can make it work, depending on how you roll.
First, if you twirl down the Options arrow, you'll see that 'Show Action When Run' is not checked; this means that if you fill in at least one recipient (as I have for demonstration purposes), Mail Man will simply open a new message, attach the files and send the message, with no further effort on your part. However, if you would like some on-the-fly control over who this message gets addressed to, or perhaps you would like to add a subject on a per-message basis, your second option here is to check that box. This will give you a dialog each time you run the action that looks remarkably similar to this:
This will let you make any changes to the message before the action completes its task. Once you click Continue, Mail Man will finish creating the Mail.app message, attach your files and send them into the wild binary yonder.
Now I typically use this action as a droplet on my desktop (or from the Dock), created by choosing File > Save As... in Automator, but it works just fine as a plug-in for the Finder and Folder Actions as well. Using it this way, you could right-click files and folders in the Finder and chose Automator > Mail Man (or whatever you chose to call it), or simply attach it as a Folder Action so you can automatically email anything you drag and drop onto a specific folder.
Either way, I hope you find Mail Man
useful, as it's good for all sorts of handy email work like archiving stuff in Gmail and shooting files to coworkers. Feel free to ask question in the comments, and I'll try to help.