u/welktickler

I am just a beginner starting out and I thought I understood push ups until I read
https://nick-e.com/push-up/
I am a bit ashamed to say this has confused me. You use you shoulders to guide the motion? Forearms straight up at all times?

I want to make sure I am doing this correctly to avoid injuries.

Can anyone dumb this down for me a bit please? Or can anyone give me other resources I could read? I have tried using a search engine but there is a vast amount of results and I don't know which site I can trust and which are to be avoided; I am a cynical old man about the internet and like to make sure I know what I can and cant not trust.