Start by reading the National Geographic page on food chains and food webs. Be ready to compare/contrast the two types of images, after your reading. 

Then watch the Crash Course video, Links in the Chain. The first part is a little bit of review, then he does go into the vocabulary you need to know. He starts talking about food webs at about 6:35.

Summarizing key things covered in the reading and video:

• a food chain models the sequence of feeding relationships
• a food web shows a complex network of feeding relationships