Sorry for the horrible font changes and how tacky this tutorial looks, but I hope you can ignore that and get something from this!
First, download Irfanview from here.
Personally, upon install I like to select the option that allows all the pictures to open via Irfanview, but you don't have to go with that option.
Step 1: Using Irfanview, open the cake photo you want to watermark. If you’ve chosen at install to have all .jpg files open in Irfanview, this will happen automatically.
File/Open/Browse for correct .jpg file