I get msg 'wait for the camera to finish recording'

When you record something like a picture of a video, the Camera writes the data into your removable Cards i.e. SD cards, CF cards etc, In cases where the File is large, such as 4K videos for instance, it could take the camera a while to write all the data into a card hence it wont allow another action i.e. taking another photo until all required data has been written to the removable card. If you are simply taking HD videos or normal photos (not 4K videos) and youre still getting this msg then your removable card might be a bottle neck, try changing your removable card to something that supports higher write rate i.e Class 10 SD card = min 10mbps) this should allow your camera to finish writing all required data to the card by the time you are ready to take your next shot.