I'm making models in Blender and, fortunately, for most of the time, I could solve the problems that I've stumbled upon.
But there truly is one particular problem that is haunting me for quite a long time now.
As you can see on the model's topology, some n-gons and T-splines (atleast I think that's what they're called) have formed. My best guess would be that when I was insetting some faces of the model, it made the topology on one side of the model different than on the other side and so these problems have formed.
The problem is present even in another object of the scene.
As you can see, these are some of the problems that truly needs to be solved before continuing or adding subdivision surface modifier. It's extremely frustrating to have this formed in all objects I did so far over and over again. Especially when the mesh gets more complicated.
I have no idea how to get these things fixed - knife, for example, seems like an extremely difficult option, also when bearing in the mind the fact that it could cut through other edges and make complete mess, so I'd have to hide all faces I wouldn't be currently cutting.
Worst of all is that the vertices which are creating the n-gons or T-splines have "reference" vertices only from one side of the model, but I can't find vertices I'd join it into on the other side of the model (via J shortcut). Bridge edge loops also doesn't seem suitable.
I'm hoping to have quad faces in all my models, but these problems are rather demotivational. Thanks everyone for responding to my question in advance.