The other window is a white screen, and this is where all your working information will come up, along with details about your databases and tables when queried.
Let's learn how to modify fields in a database table, using phpMyAdmin. Select on the table to modify by clicking on it. The right window will open up with the details of the table, including a list of all the fields in the table. Find the field you wish to modify. Start by placing a check mark in the box at the beginning of the field row. Then click on the Change icon, which is below the list, and looks like a pencil writing. This will open the selected field line by itself, and you can now make the changes you need to make. Click on Save when you are done.
The right hand screen will now show that the table has been successfully altered, and will show the change. You can click on the HOME button, which is in the left panel, below the phpMyAdmin name, and return to the main screen.