How to make use of myfitnesspal?

on the website
my home > profile > edit photos
takes you to where you can upload pictures for your profile

for the forums.. .you posted this on the forums but...
community > message boards
takes you simply to the table of contents, you need to tell the system which board your post is related to IE if you're posting a "Hi I'm X..." then you may want to click the "introduce yourself" forum... if you're posting a family favorite recipe then you may want to click the "recipes" forum... once you're ON the forum related to what you want to post you'll see the green take action "new topic" button

Apps can change what your active profile picture is, but I think they are limited to replacing the existing photo, if you want multiple you need to get them uploaded via the computer.