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If you google visceral and parietal you get: The parietal layers of the membranes line the walls of the body cavity (pariet- refers to a cavity wall). The visceral layer of the membrane covers the organs (the viscera).
but
the first image that pops up is this :
I don't understand how the inner layer is covering and the outer is lining ?
Yes, the parietal pleura is on the wall of the thorax. That picture isn't great. Each lung has its own pleural cavity, ie its own visceral+parietal. Another important thing is the folding over. Imagine the parietal pleura running along the inside of the ribcage...when it gets to the middle of the chest (the mediastinum), it folds over, or "turns the corner", and is now the visceral pleural running along the surface of the lungs. The pericardium functions similarly, and so does the peritoneum/mesentery. Here's another diagram that could help: 
