Ok, I'll try to walk you through this. It's freeware, and as such, has no instructions and no help and it's not very intuitive.
1. Open PicMark
2. Under the "Window" menu, select "Watermarks manager"
3. You should see a box with stuff
4. At the bottom left, click the "+" button
5. You should now be able to type in a name for a watermark in the "Name" field at the top right
6. Type in the "text" field what you want your watermark to be
7. Customize it by choosing a font in the "font" drop down, and choose color, italics, bold, etc.
8. Use the slider below the text to select size (what you see is much larger than what actually shows up in your picture)
9. Click "update preview"
Your watermark should now be set to go
Now, to watermark pictures, go back to the "window" drop down menu and select "Workshop". Sometimes this window is hiding behind the manager window, and if you just drag the manager window to the side, the workshop window is there behind it.
1. Choose the "File" drop down menu, and select "Choose picture..."
2. Navigate the new finder window to find the picture you're looking for
3. Click "Open" the picture file reference should now be in the workshop list.
Now you can choose your watermark by clicking on the watermark that follows the "Watermark:" text, or just leave it at the one it defaulted to if that's the one you want.
4. Click "start"
5 In the dialogue box that pops up, choose a destination for the watermarked picture.
That's it.
One word of caution, before you do this, go into "Picmark" drop down menu, select preferences, and check the "watermark pictures remain just references to original file" selection. I think if you do that, you don't alter your original file, or clog your hard drive with duplicate image files, but I'm not certain about that.
Hope this helps.
Let me know if you have other questions.
Regards,
Boris