There are two simple ways to post images and videos right into your post!
Here they are:
1. If posting an image that's already hosted somewhere online (an image or a video that you saw on another website that you'd like to share with us, for instance):
-- Click on the yellow box with an image of mountains on it, in the lower one of the two rows at the top of your "Reply" text window (located on the right side of the lower row, fifth image from the right).
-- A window will pop up, asking you to enter the link of your image. Once you copy and paste the link of the image into that window, the photo will be posted directly into your post.
Done! 
2. If posting an image that's located on your computer hard drive and not hosted anywhere online, you can easily host it directly on this website by doing the following:
-- Click on the paper clip icon located in the top row of the text options at the top of your "Reply" text window (it's on the right side of the top row, fourth image from the right).
-- A window will pop up giving you the option to upload an image from your computer (the top one of the two options). Click on the "Choose File" button, locate the file you'd like to upload on your hard drive, and click on the "Upload" button.
-- Once you've uploaded any images you'd like to insert, close that window and click on the arrow to the right of the paper clip. All images uploaded will be displayed in a drop-down tab.
-- Click on any images you'd to like to embed in your post, and they'll be posted directly into it.
Done! 
Hope this helps; holler if you're having any difficulties!