You can check if your Pixel is active by looking at the top right corner of Your Dashboard the green circle indicates that it's active, and the red circle below indicates that the Pixel isn't active.
If it's not active, this would either mean that you have to Install your Pixel or it isn't correctly installed.
To check other Pixel, click on the box to have an overview of all the pixels you have created
You can also see it in the 1st step of the "Get started" board in Your Dashboard
Advanced TIP: You can also check if your pixel is active by opening the console on your browser (by right clicking on the screen and selecting 'Inspect') and typing sfpid, if the pixel is properly installed, the console will return the pixel id number