How do I remove those lines around that circle. If I erase them all the face around the circle will disappear.
It’s hard to tell what it could be without a blend file, but my guess is that you have an ngon (shape with more than four sides) where you placed the cut out. ngons can lead to shading issues if the surface isn’t completely flat.
If that is the case, then you should read this thread: https://blenderartists.org/t/need-help-modeling-a-circle-inset-on-a-slanted-surface/
try bevelling the circle’s edge, or putting an edge loop around it.
i think the way i model this is, create a triangle (low poly), use the boolean modifier to create a hole then use subdiv to make it smooth. I think the rest on how the polygon will look like will depend on your choice.
Try applying auto smooth in the geometry tab. By the looks of the shading, smoothing is applied, but it doesn’t need to be on the flat surfaces, so auto smooth with an angle of 30 will probably look better.