To restart the camera, just switch it off and on again. Or remove the battery, replace and switch on again.

Unfortunately that rarely clears the dreaded lens error. Has the camera suffered any kind of accident? Does the lens open at all?

If the lens is sticking this can sometimes be due to dirt between the lens barrel sections. There are a few ways of cleaning it.

If that’s not the case then just about the only option is to get another camera of the same model with a different fault (they go for a small fraction of the original purchase price) and cannibalise one to fix the other. Typically, a compact camera contains 2 motors in the lens and several sensors to measure the motion they produce. If the output of the sensors isn’t consistent with what the camera commanded the motors to do then you get a “lens error”, which hence can have various causes. It might in principle be fixable but disassembling a lens is pretty difficult. Correction: reassembling a disassembled lens can take the patience of Job!