In short the kid learn based on his interests and does activities / games to learn new topic.

there are other aspects like colaboration between kids etc

Might I missed things

Montessori is a method of education where kids are in classes with mixed ages (but grouped) so they learn leadership, community. Lessons are interactive, proof of work based really, and largely self-directed (within the context of the “lessons” that are usually interpreted as play. Personal responsibility, everything gets put back just as they found it by themselves for the next person. Independence, creativity, freedom, and regard for the uniqueness of each child are emphasized. I love it.