Outro: a small clip that runs at the end of the videos and asks customer to like and subscribe. It is also used to show related videos of your channel.
Your Youtube Channel should be a brand in itself. It should have a logo, a thumbnail and catchy brand name. Apart from that the videos should have intro and outro.
Intro: 3-5 second clip that runs at the start of each video. Intro focuses on building your brand in your audience minds through consistent bombardment.