How to know doubts and clear them?

Two ways, I think, you solve or ask other help

It's simple, study , learn... then act.

You need to ask questions, research on the exact thing that brings doubts and analyze the topic and read more on it

Hey, Dan Mars, firstly you should analyze and read a topic then, to clear your doubts you should deeply understand the topic and research that topic.

Analyze the topic and try to grow your interest in the topic then it's very easy to have understand where you have doubt write them and ask an expert for the soultions

You need to listen to your inner call.