This is quite simple in many cases. If the camera streams a format that VLC can grok, then you can just use the VLC app. Additionally, you might be able to view MJPEG in a web browser. You can stream MJPEG from a USB camera with a Raspberry Pi. This is typically used for 3d printer monitoring, but can be applied to most cases where a slight latency is OK.
So if I am right, the camera sends signal to transmitter, and the transmittr signal i can see on website with MJPEG?
Yes, that's correct in the case that the camera is a USB camera or in other ways isn't a network camera (e.g. analog video out). The format that the transmitter sends depends on the transmitter's design and setup.