I am doing this Blenderguru tutorial to work on my modelling skills. There is a weird bubble next to that black circle. What is the reason for that and how to solve that (I already did smooth shading) ?
This is caused by uneven topology. you need to make all of the topology on the front of the phone flat. We will use vertex snapping to fix this problem. First, select the edge loop that borders the camera, but not the one that actually makes the indent.
Now we need to enable vertex snapping. You can enable snapping by clicking on the magnet in the 3D window bar. Alternately, Shift+Tab will also turn snapping on. Now you need to change the type to "Vertex" Do this by open the pop-up next to the magnet in the 3D window bar and selecting the cube with the two white vertices.
Now all you need to do is grab the loop along the "Y" axis (G>Y) and mouse over the next largest loop to bring them even.
an orange circle will appear to tell you where you are mosing over to snap.