For your profile picture you just go to your profile on QL and choose to upload a photo. It will open all the files on your computer so you can choose which photo to use from them.

It's a bit more complicated to post a photo in a thread. First you need an account on a photo sharing site such as www.photobucket.com or something similar. Once you have uploaded the photo on that site, you can choose a link to that photo which you can copy and paste into your post in QL that will inbed a photo into your post.