It seems you are asking for a guide on (often referred to as Bijoy Bayanno), the most popular Bengali keyboard layout and typing software for Windows.
In the early 1990s, (founder of Ananda Computers) sought to create a simple, accessible solution. The result was Bijoy Bangla Software , built around a keyboard layout called Bijoy 52 . It used a technique reminiscent of old typewriters: each key produced a fixed character. For example: bijoy 52
Better: Print a Bijoy 52 keyboard sticker or keep a reference image open. It seems you are asking for a guide
Example : To type , press k + g + l (assuming standard mapping for ক and ত). Useful Resources bijoy 52