Resources for Amazon Selling

Looking to get into selling in Amazon in the UK. Struggling to find a resource that can help with guidance to get started.

I am seeing a lot of online tools but all of them are paid and I am skeptical of spending money on those. I would rather put hard work and manual research rather than pay for a tool at this stage.

Any online resource or YouTube guide that is recommended? Finding it hard to weed through the amount of people selling Amazon as a get rich quick scheme or selling their courses.