The camera clearly indicates when it's using its tiny internal memory. It even displays a warning message after you switch it on.
With RAW enabled, there's only room for 1 single RAW shot. You can always redevelop the RAW in-camera once you add a memory card, or off camera with Lightroom etc., both in full-size glory.
Or simply disable RAW, and you can shoot and internally store 4 frames in JPEG FINE size L. Or more smaller shots. Per default, the camera chooses an option that lets you shoot as many images as possible. Internal memory is an emergency mode. Many use it to shoot their business card or address, so if the camera is lost and found, you have a simple way of proving that it's yours (and a means of telling the finder how to contact you).