Before long the No Smoking light will go out. The plane will continue to climb until it reaches its flight level and the Fasten Seatbelts sign will then also go out. Flying In normal flight, you can move around the cabin freely. It's a pretty good idea to stretch your legs occasionally. If there is going to be turbulence you may be asked to return to your seat and fasten your seat belt.
Some turbulence is mild, but sometimes it's a horrible experience.
On a flight back from America once, the turbulence meant that no one could leave his or her seat for two hours. Everyone was being thrown around in his or her seat quite violently. There might be times when you are convinced that the plane is doomed. But all the noise and bumpiness are perfectly normal and just a part of everyday flying. After a few flights you will stop worrying about odd noises, and just accept that odd noises happen.