How do I make short video.mov files into one video?

I have a digital camera that takes video but only 15 sec .
I want to join several video files together to make one video
How can I do it ( with out buying any extra software).
I have the full NERO software and some conversion software
My video file seem to be ?????. MOV typesand my camera is
Nikon 775

windows movie maker

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easy video joiner