Simply a way

A mind map is simply a way of generating ideas...

I think it should be write like this:

A mind map is a simple way of generating ideas...

I copy it from: http://www.britishcouncil.org/professionals-exams-ielts-academic-4b.htm (the 6th paragraph)

It make me confused! Please explain!

First of all, if you're quoting someone, then you should put their words in quotes. Also, it's "I think it should be written like this", not "I think it should be write like this", and "It confuses me", not "It make me confused".

As for your question, "simply" is an adverb, and adverb modify verbs, adjectives, and other adverbs, so here it is modifying "is". "Simple" is an adjective, and adjectives modify nouns, so it would modify "way". The sentence is not saying that the way is simple, it's saying that "a mind map is a way" is simple. Do you understand the difference between "I slowly bought a car" and "I bought a slow car?"