Some interesting videos:
“Introduction to Literary Theory: Major Critics and Movements” by Ellie Green who is a professor for English Literature at Princeton University, USA.
Short intro to Marxism by a group called the Curious Classroom
Intro to Post-Colonialism by a Christopher Flynn who is a humanities professor at St. Edward’s University located in Austin, Texas, USA.
Funny take on modern Colonialism by Trevor Noah
Anti-Colonialism in Africa by Prof. Carol Anderson is professor of African American Studies at Emory University.
Timeline of literary theory: a diagram of theories
Nice PPT about how to use theories when you read texts: Literary theory
A good introduction to literary theory and schools of criticism by Purdue OWL
If you want to read up on theories, this is a good book: Beginning Theory: An Introduction to Literary and Cultural Theory written by Peter Barry.