Next time, if you need some information about crypto, try to search on the Google first...
There are so many articles that you can find on Google...

Here some article that can answer your question about ERC-20 Token :

• https://www.investopedia.com/news/what-erc20-and-what-does-it-mean-ethereum/
• https://en.wikipedia.org/wiki/ERC20
• https://www.cryptoniam.com/what-is-erc20/
• https://99bitcoins.com/what-are-erc-20-tokens/
• https://coinsutra.com/what-is-erc20-token/

and here video explanation about ERC-20 :

https://www.youtube.com/watch?v=1tSpSXCxFbg