hey i am new here and new to 3d modeling ^_^

i try to model a tower in maya and open a door in it but i get bad shading in the door frame i dont know why this happen can someone help me to learn i will search about it if i know what is the problem

Edit: i am study 3d by my own i never got to any school so i hope someone point me where i learn about this more and what is it when i add any line to any curved object i got obvious line on the geometry thank you