how to put a picture into a placeholder

I just purchased my first after effects video from ponds and would like to know how I would put a video or photo into the placeholder. Is there a tutorial on the website that would explain? Thank you!

Open placeholder composition, drag'n drop your picture inside composition, that should work. If you have any problems Contact author, or read help file.

If it's a "footage placeholder" you should be able to right click > replace footage < file from the Project window.

or hightlight the layer you want to replace and press "alt" and drag and drop the new material onto the highlighted layer . .

Here i would like to show an another tool that works simply but in the effective way. Check out the latest Image Placeholder tool introduced by CSSChopper.
Use it at : http://lab.csschopper.com/placeholder/
To know more details : http://www.webgranth.com/image-placeholder-free-online-tool-to-generate-dummy-picture