OT: how to restore my Mac?

[Tiemo Hollmann TB]

Hi,

I've just messed up my Mac. I executed by accident chmod in my root and gave
all users all permissions to all my files (what I actually didn't wanted).

I am not used to Macs, so what is the easiest way to restore all file
permissions? Is there any kind of "reset to factory settings" or what about
a restore from time machine, will that restore the file permissions, if the
files are older, or do I have to reinstall the system from scratch and if
how?

Thanks for any hints

Tiemo