If i lost on stocks i bought and sold in 2021, how is that treated ?

You should have received a 1099-B from your broker reporting the stock sale.  

You are in the Online version, so I will focus on that.

Go to Wages & Income

1. Scroll to Investments and Savings
2. Select Stocks, Cryptocurrency, Mutual Funds, Bonds, Other (1099-B)
3. Time to kick off your investments! = Okay
4. Relax. We got it.= Continue
5. Let's import your tax info = Enter a different way
6. Select what you want to post from the 5 boxes.
7. Select Stocks, Bonds, Mutual Funds = Continue
8. Enter the bank or brokerage = Continue
9. Tell us about the sales on your m 1099‑B = Answer questions
10. Now, choose how to enter your sales = One by one
11. Post your information