On my Technika SH-340T when I switch it on ''protected card'' comes up on the screen. What can I do about this?

This is a general problem, not specific to your camera.

Inside your camera, there's a memory card. In your case an SD card. This card has a slider that can be toggled between two positions. Your card's slider is in the "protected" position, and means you can't write to the card. This position is used when you want to be sure you don't overwrite important files (in your case pictures).

The sliders on these cards sometimes change positions when you jam them into a card reader - which might be what happened here?

Simply take the card out, find the slider, and slide it over to the other position. Insert it into the camera, taking care to not slide it into the protected position again, and you should be all set to take pictures!