First you need a videomaking program. If you have Windows on your computer/laptop I bet you have a program called Windows Movie Maker as well (If you have a Mac, it might have Final Cut Express installed). It's not so good, but it's easy and good to make your first video in. (If you want a better program you can download Sony Vegas.)
After you've checked that you have a videoediting program you can download clips. You can either download full episodes using a download program or you can go on different Jensen or Jared fansites on the internet to download them.
Here are some sites you can get clips from:
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link
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Just search for either "Jensen Ackles Fansite" or "Jared Padalecki Fansite" on Google, and it'll show up different fansites you can download clips from :)
Hope this helped.
