If you don't want to make your space available on certain days of the week, go to your listing editing interface:
Click the "Host" button at the top right of your screen
Select "My Listings"
Click "Edit"
Select the "Availability" tab
At the top of the page, you'll see a weekly schedule where you can click on days and mark them in blue for days your space is available, and in white for days it's not available. You can also specify the time slots during which you want to make your space available.