3d modelling help needed

Hi,
I am a beginer 3d modeller. I use Lightwave, but I guess this thing almost works in the same way at every programs. So here is this casette recorder. As you see there are some lines in the model which are not needed and wasn't drawn by me. So how can I destroy them and why are they there???
Another -or the same- problem you can see on the rendered picture. The sides should be plane, but on the upper part you see that bug...
I am a beginer 3d modeller. I use Lightwave, but I guess this thing almost works in the same way at every programs. So here is this casette recorder. As you see there are some lines in the model which are not needed and wasn't drawn by me. So how can I destroy them and why are they there???
Another -or the same- problem you can see on the rendered picture. The sides should be plane, but on the upper part you see that bug...