getting started with multisite

Helle everyone, I’m planning to build a website which will be just like this:
exemplegroup.com(static)
exemplegroup.com/group1 (which will have it own menu and template like a normal website)
exemplegroup.com/group2 (which will have it own menu and template like a normal website)
exemplegroup.com/group3 (which will have it own menu and template like a normal website)

for this do i need a multisite?? where can i start it? Thank you for your help.