Multiple ways to wipe config.
1- >request system zeroize
2 #load override factory-default and tweak from scratch
3 if you are logged in to the console port, delete all interfaces, delete all vlans, all protocols, polices and firewall filters , commit them start from scratch
unit represents a . so you can add a subinterface. Basically you can logically partition an interface like you would a harddrive. In this case only a single unit is valid and is used for ethernet-switching and that is unit 0. If you load the factory default, you have to rename switch, set root password, add your user accounts and then create your vlans and add interfaces to vlans. Create trunk ports and add vlans, set up our management interface for oob management.
When you add interfaces to vlans, you can add the interface under the vlan heirarchy or add the vlan to the interface interface-mode. Chose one and use it.
If you chose to add interfaces to ethernet-switching manually, you can use configuration groups, but if you do, then it it best to standardize this throughout the network.
You can add interfaces one at a time or use interface-range or a combination
You can save the config from either config or operational mode.
In config you can simply save from the top of heirarchy to a filename of your choice and to the path you want to save the file. In config mode, you can also use: show | display set | save <filename>
Pick your poison.