Fitting requires an understanding of how the weapons, tank , propulsion and engineering modules and skills interact. Articles from several years ago are still relevant - CCP has adjustes some stats to improve balance but the fundamentals remain the same.
Many of the articles recommend a 3rd party tool called EFT (Eve Fitting Tool) which is no longer supported by it’s developer. The currently supported 3rd party fitting tool is
If you join a combat oriented corporation, they will generally have a selection of doctrine fits designed by their fleet commanders - typically these are posted on http://fleet-up.com/ however you can generally see what people are flying by looking at the kill reports on https://zkillboard.com/ This page discusses this Fitting A Ship (Working Example) - EVE University Wiki