The language itself is simple[1] but the environment and tools aren't. Smalltalk is a world in itself which is both its strength and weakness.
Nevertheless, I find the argument on their website kinda odd and a bit confusing. I mean, I see a lot of Smalltalk advocates claiming the language is so simple to learn and at the same time I see a lot of programmers having trouble learning it.
Maybe it is just wrong to call it 'very easy to learn' just because the syntax is simple.
I think the first important step, is to understand the different columns of the 'System Browser'. From a quick search that video playlist might help you:
https://www.youtube.com/watch?v=0xF4fnGaE2w&list=PLqbtQ7OkSt...
"The only languages worth learning are those that change the way you think about programming."
Doing serious work is demanding.
But so is serious work in any environment.