Microsoft has done a really good job with documenting eCommerce development on the Microsoft docs site.
Here I am just summarising useful links for those wanting to get started with development.
Start by watching some of these videos. Some are repeating content but very useful information in all of them.Accelerate your business with Dynamics 365 Commerce
Dynamics 365 Commerce – What’s New
Next, I suggest getting onto the forums if you need help Dynamics 365 Commerce Forum.
There is an insiders yammer channel "Finance and Operations Insider Program". Join the "Retail interest group". I won't post the link here but this is helpful to connect with Microsoft employees who built the solution.
Last but not least. I would recommend Commerce In A Day session. It is a hands on lab sessions.
Hope this helps those starting their learning journey.