I've been doing go to market for technology businesses to some degree for the better part of 20 years now and I still learn more every day. I don't really see it as something you can easily learn by reading about, mostly because there is a lot of nuance.

That said, it basically boils down to 3 things:

Personas

Channels

Messages

You have an archetype of someone in your head that would like your tool, you want to test if that archetype exists. That persona likely consumes content, your job then is to understand the channels that persona typically likes to consume their content, and try to serve them a message they can understand in the time you have to serve it. There are thousands of personas in millions of channels consuming billions of messages, that is why it's hard.