"Freezing", sometimes called "Locking", your rows is a great way to compare specific rows to the rest of your data. I will show you how to use this technique in three simple steps.
Step #1: Select the Row
First, you will click anywhere on the row that you want to freeze.
You can also click and drag the grey bar at the bottom of the "A1" cell to select what rows are frozen, as well.
Step #2: "View" --> "Freeze"
Next, simply open the "View" drop-down menu and select the "Freeze" tool. That will lead you to the second menu, which will let you specify how you want to freeze your rows.
I usually like to select the "Up to Current Row" option.
Step #3: Make Sure it Works
Lastly, you will need to scroll through your data and verify that the freeze actually worked. As you can see in the example image, the row you froze will stay on screen as you scroll down, but the rest of the data will continue to scroll down normally.
And that is how you freeze rows in Google Sheets.