[ASK] width remains the same despite the different forums screen size [help me]

[player378]

how are you

please help me
I find it difficult

I would like to inquire about the width of the forum.
width will remain the same despite using:
- Monitor 14 inch, 15 inch, 17 inch, 18 inch & blabla .....
- Laptop LCD 10 inch, 14 inch, 15 inch
and all types of computer screens

width will remain the same, as the following figure

https://vborg.vbsupport.ru/external/2013/07/26.png

how do it so that the width of the forum remain the same, although different monitor sizes
help me

im a newbie