Sharepoint site customizations

Hello Everyboy,

I'm working on a POC with project and sharepoint online.

I've configure sharepoint in order to create a sharepoint site when a project is published. It's work fine.

Now, i would like to customize some items on my site like, left navigation bar, create default folders in document library, add a site mailbox by default.

I don't know where i can do that ?

Do you have some documentations about project and sharepoint customization ?

Thanks a lot,