Decals/Stickers...What I need to know

I am VERY new to truck owning and I have a really novice question. I want to add a couple stickers/decals (whatever they should be called) to the back window of my extended cab. I have never done this before and need to know if there is a special material I need to look for with these stickers/decals? Also, should they be applied from the inside of the truck or the outside?
Thanks for any advice you can offer.

 

apply them on the outside but i dont think theres really a special type of decal you need to look for. make sure you clean the glass well before installign the decal and make sure the glass is dry.

 

Condition 1 Industries makes quality vinyl stickers.

http://condition1industries.com/index.php?main_page=product_info&cPath=1_9&products_id=12

 

https://www.carstickers.com/instructions.php