From Forum Nokia Wiki

There are various ways to transfer an application to a phone:

• By connecting the phone to a PC using the appropriate connectivity hardware and software (PC Connect, Bluetooth or IR)
• Sending the application by Bluetooth, IR or SMS from another phone
• Sending the application to the phone by email
• Downloading it onto the phone over the internet (OTI)
• Over the air (OTA) distribution
• If the handset supports removable media cards, you can use a card reader to copy the installation file from the PC and install the application onto the phone from the card. The application can still be installed to the phone’s internal memory and does not necessarily need to be installed to the card itself.

Installation Files

Regardless of how the application is delivered to the phone, it can only be installed using a .sis installation file ("sis" stands for Symbian OS Installation System). These files are also sometimes described as sisx files because the installation file format has been changed and extended in Symbian 9.1 from the original sis file format of previous versions of Symbian OS.

The Symbian OS software installer uses this installation file to control which files are installed onto the phone and restrict installation of those which require privileged access to system services and data to those it can verify as ‘trusted’.

A PC-based tool called CreateSIS, located in the epoc32\tools\ directory, is used to create an installation sis file. CreateSIS is a wrapper around three separate tools which may alternatively be used separately:

• MakeSIS, which creates a .sis file from a text-based .pkg file
• SignSIS, the installation file signer
• MakeKeys, the certificate generator.

The following diagram illustrates the use of these tools:

CreateSIS takes as input a package file (.pkg extension), which you create to specify which application files (executable files and resources) need to be installed onto the phone. The package file has a list of where the files are located on the PC, that is, the locations to which they were built as part of the ARMV5 or GCCE builds, and the location to which they must be installed. Optionally, CreateSIS also takes a developer certificate and private key as input, to output a signed sis file.