First is first. Check your wallet.

Lets check how many steem dollars you have.

In your case about 22 dollars. good enough.

Next unto your upper right corner near the avatar menu. Click that 3 bar symbol. Then a dropdown list will be pop up.

From that, select market and click on it.

To the right are the prices people are ASKING people to pay for steam. To the left is people who have posted BUY orders and are hoping people will sell to them for that price. (you can play the market if you like)

Decide how much you are willing to pay in steem dollars and in the section under the left type the price you are willing to pay for each steem dollar into the PRICE field.

Skip the Amount and just type the amount of STEEM DOLLARS you wish to convert into the TOTAL field. It will automatically calculate the amount for you from there.

Click BUY STEEM. This will pay a market order. If someone is interested it will happen almost instantly.

If they don't buy it instantly it will show up under open orders that also has a CANCEL link you can use to cancel it.

Then check back your wallet.

You got STEEM.

Then, select steem from the right side of it and select power up.

Cheers.