[Xperia Z Android Development] umarian:
About instal RomAur from recovery some informations about Android partition and CWM is very usefull:

/BOOT:this is the partition that enables the phone to boot, as the name suggests. It includes the kernel and the ramdisk. Without this partition, the device will simply not be able to boot. Wiping this partition from recovery should only be done if absolutely required and once done, the device must NOT be rebooted before installing a new one, which can be done by installing a ROM that includes a /boot partition.

/SYSTEM:This partition basically contains the entire operating system, other than the kernel and the ramdisk. This includes the Android user interface as well as all the system applications that come pre-installed on the device. Wiping this partition will remove Android from the device without rendering it unbootable, and you will still be able to put the phone into recovery or bootloader mode to install a new ROM.

/DATA:Also called userdata, the data partition contains the user’s data – this is where your contacts, messages, settings and apps that you have installed go. Wiping this partition essentially performs a factory reset on your device, restoring it to the way it was when you first booted it, or the way it was after the last official or custom ROM installation. When you perform a wipe data/factory reset from recovery, it is this partition that you are wiping.

/CACHE:This is the partition where Android stores frequently accessed data and app components. Wiping the cache doesn’t effect your personal data but simply gets rid of the existing data there, which gets automatically rebuilt as you continue using the device.

/SDCARD:This is not a partition on the internal memory of the device but rather the SD card. In terms of usage, this is your storage space to use as you see fit, to store your media, documents, ROMs etc. on it. Wiping it is perfectly safe as long as you backup all the data you require from it, to your computer first. Though several user-installed apps save their data and settings on the SD card and wiping this partition will make you lose all that data.

/SD-EXTt:This is not a standard Android partition, but has become popular in the custom ROM scene. It is basically an additional partition on your SD card that acts as the /data partition when used with certain ROMs that have special features called APP2SD+ or data2ext enabled. It is especially useful on devices with little internal memory allotted to the /data partition. Thus, users who want to install more programs than the internal memory allows can make this partition and use it with a custom ROM that supports this feature, to get additional storage for installing their apps. Wiping this partition is essentially the same as wiping the /data partition – you lose your contacts, SMS, market apps and settings.

Now about CWM:

-wipe data/factory reset

This option wipes all user data on the device as well as cache. Doing this will leave your phone in the state it was in when you bought it or when any custom ROM was first installed. It will also wipe any sd-ext partition that you might have setup . Selecting pretty much any operation in ClockworMod (including this one) will bring up a confirmation prompt that can save you from a lot of potential trouble in case you accidentally select the wrong operation.

-wipe cache partition

Wipes the cache partition of the device to clear all the data accumulated there over use. This is often used before installing a new ROM, app, kernel or any similar mod via recovery.

-wipe dalvik cache

Allows you to wipe the cache for the Dalvik virtual machine (the custom-built Java virtual machine for Android).This is required before most ROM installations and at other occasions too, for fixing some problems.

fix permissions

-Fixes the file permissions for the internal memory partitions back to default. This is very useful as a fix for several errors and Force-Closes that start appearing after you or an application you installed and provided root access end up messing up the permissions of important files.

I hope this informations is usefull for a good instalation for a new rom.