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How does online platforms give real time quotes

Online platforms like Xometry, protolab uk, etc give real time costing on the basis of file uploaded and other parameters selected in a user form through the website.

can anyone break down the whole process they are using.
How many parts/steps in the whole process should be there 
How many layers should be there
What should be the data flow

I am not from the technical(IT) domain, I could make out they they need ERP to save all costings, CAD program to read the CAD file and take user input from Form THEN combine this from material + machine + manpower costing from ERP to give the costing.

so 3 main part 
1. front end - web application for user input
2. CAD program for all calculations
3. ERP for all manufacturing related cost input

Please help how it should be pulled of technically 

Sorry I am a complete novice when it comes to technical IT part.

would be really grateful if some one can simplify the technical implementation that can pull this.