How do you upload a video or picture in this website? What are the tips?

The only thing I'll add is that I edit mine to keep the size down. In Windows all you need to do is right click the image on your desktop, select Edit from the context menu, and you can crop, resize, or do a few other alterations. Doesn't need special software.

Dunno what you'd have to do with Apple but there's bound to be a similar option.