I need to get well organised excel platform with analysis.

Hello, I have a small clothing business based on the Instagram platform. I am a beginner in excel and I developed excel but it's not organised at all so I would like to fix that.
* every time I want to calculate the cost I write the cost of specific thing for example code 1 cost 300 and each time I have customer ordering code 1 I need to find out how much code 1 costs in 50 different codes. I am sure there is a way when I write code 1 it writes its price straight away.
* In excel there are many different advertisements I want a brief analysis of selling in relation to advertisements (Promotions).
*organise it with good order even if you will use separate sheets
* I want estimations in the analysis like for example if I double the promotions how much I would probably profit
* i want you to develop that excel automatically says which code is the best selling.
* you might find there are many things in my excel and it might be little complicated please if you need any clarifications contact me as soon as possible i would be happy to help.