Click on "Go Advanced" then on "Manage Attachments" then on "Add Files" then on "Select Files" then find/select the photos in your computer then click on "Open". Ok, you are almost done! Click on "Upload Files" and then you can opt to "Preview Post" before "Submit Reply". There are a few minor other ways to do it but this is the way by trial & error that I do it. Your photos will automatically be sized. No need to do it before you upload them. There is a limit on the number per post but not per thread. Good luck & let me know if you have more questions.
Ed