Line 12 on Schedule SE

Hello, 

this may sound very ignorant, but I just noticed line 12 on Schedule SE: 

"Self-employment tax. Add lines 10 and 11. Enter here and on Schedule 2 (Form 1040), line 4 ."


What is Schedule 2 and do I need to file it if I'm filing jointly for 2020 taxes?  I started freelancing in 2019 and didn't file this Schedule last year. Should I be worried and what is this schedule used for? 

 

Thanks in advance for anyone who responds to my message. 

 

🤗