Licensing is simply giving another person or business the right to use your property with certain conditions for a fee. In the online space, this is usually copyright-protected works (like photos, videos or an online course or membership) or trademarks (like a brand logo).
If you are a creator of content, learning about content will help you understand how to protect your content but also what rights to offer in order to scale and grow.
If you want to use other people's content or brand, learning about licensing will help you understand what to look for in a licensing relationship.
I get many questions about licensing from physical product creators as well (like crafters and makers) who want to give some limited rights to their creations to other people or businesses to use for a fee.
When you listen to your new favourite tune on Spotify or Apple Music, you are using the music pursuant to certain licensing terms. Same when you purchase a stock photo or make an image on Canva.