Why is this bad topology happening i was trying to create my first room art , i started with a cube , deleting its one vertex , then i extruded three faces , finally , i started to model a sofa , but then i figured this bad topology at the corner of the sofas hand-rest

i tried to fix by changing the technique of miking it , earlier i  made by extruding the face , but then i also tried extruding edges , but the problem doesn't seem to vanish , here is a better shot in edit mode

the problem doesnt exist in edit mode
here is the file
There are a lot of faces overlapping, or vertices that seem to be part of a face but actually are not, etc, you didn't model it the right way. Also, as pointed out by Lemon, you use a Mirror modifier but your mesh go beyond the center of the mirroring. Maybe re-do it from scratch, and maybe follow some basic tutorials about modeling.
If I just take one example: If I select this vertex...

... and then move it...

... we can see that it was not part of the face.