I'm making a preview for my newest head. How do you put words on it? Also, I have my own logo. How do I put my logo in the pic?

Open the picture in a graphics editing software. I prefer Gimp or photoshop because they have alpha channeling.
Once you have opened the pic in photoshop or gimp, choose the text tool. It's icon looks like an "A". Now choose the place where you want to add the text. Once you have done writing the text, it will create a new text layer. Merge the layers and save the pic.

Or you can go to PicFont and follow the instructions. I prefer this method since it is easier.

Thanks Akmal.