Click on the "Compare Games" panel and input the first game you want to compare, then click on the option on the right part of the panel, it should say something along the lines of just this one (will depend on the language of your device)

Then, write the title of another game, but this time click on the box on the left side of the panel.

Repeat step 2 for any further games.

Click and hold on the slider to select how many weeks since launch you want to see on the graph, manipulating it will also modify the tables above it.