We get a lot of questions about installation numbers, keys, license number, etc. So here is the answer to your queries.

When you become a new SAP customer, SAP assigns you a customer number. This number is like any other customer number you assign your own customers, or that companies assign to you. It uniquely identifies your company to SAP. 

Once you sign your software license, each of the SAP components you purchase is assign an installation number. So, you signed a mySAP.com Business Suite license? Then you will be assigned an installation number for R/3, another installation number for BW, another installation number for CRM, etc. You also signed a license for KW? That would be another installation number. SAP sometimes splits existing products out to other divisions, so you may even be assigned a second customer number with new installation numbers assigned under that number. SAP did that with Enterprise Portals. An installation number identifies a customer's SAP component. If you open a problem under your R/3 installation number, SAP knows that the problem is going to deal with R/3 and not CRM, BW, etc. 

A few weeks later, SAP shipped your installation kits and you installed R/3. Four weeks later your users get a message saying that the license has expired. But you signed your license agreement! When an SAP instance is installed, it gets assigned a temporary license key that is good for approximately four weeks. You need to request a permanent license key as soon as you finish your installation of the SAP instance. How? First, you will need your hardware key. This identifies your operating system information so SAP can generate a key that is not only good for your SAP version but for your hardware as well. To see your hardware key, log on as adm and go to a command prompt. Type "saplicense -get" and your hardware key will be displayed. Jot it down, you will need it later. The hardware key for NT is different than, for example, the hardware key for AIX. So if you change your SAP license from AIX to NT, you will need to make sure that your company is attached to the new hardware key or you won't be able to request new permanent license keys. 

To request your new permanent license key, go to http://service.sap.com/licensekey. Use this website to give SAP information on which SAP flavor your have installed. You will have to provide your hardware key as well. SAP will generate the new key and e-mail you a text file. Save the text file on your SAP server, log on as adm, and go to a command prompt. Type "saplicense -install ifile=  ". Your key should be installed! In later versions of R/3, you can use the slicense transaction as well. 

Now your system is flying! But your ABAPers sign on for the first time, and they need to add a new program to upload master data. When they enter se38 they get a message asking for their developer key. This key is generated by SAP as well, and is used to register your superusers who will be responsible for adding new code and changing SAP-owned code. Go to http://service.sap.com/sscr to register your programmers. Once you have the developer key, give it to your ABAPer and he can enter it into the system. He will only have to supply it once per SAP instance. 

Now your ABAPers are cranking out code, your system is humming, and then! Pow! The dreaded short dump hits you when you aren't looking. You look up the error code and find a valid OSS note to fix the problem. You log on to apply the advance correction, your give yourself a developer key,

go to transaction se37, but a new popup won't go away, it keeps asking for an access key for R3TR FUGR XXXXXXXXXXXXXXXXX. You must get an object key in order to modify an SAP-owned object. Since SAP owns all the ABAP code that comes with the SAP instance, you have to get a key in order to apply the advance correction. Again, you would use http://service.sap.com/sscr, this time to generate an object key. 

All this SAP website access also demands that you have an OSS User ID, or as it is now known, SAP Service Marketplace User ID. The user ID to perform the tasks outlined in this message must have administration rights. Your should have received your primary OSS ID when you got your SAP license. If you have not received a primary OSS ID, or your SAP reseller seems to have control of your primary OSS ID, contact SAP AG to resolve the problem. Your OSS ID is connected to your SAP customer number, so if you have two customer numbers, you will receive two OSS IDs. 

SAP has recently complicated the license scenario by introducing user licenses. Do not confuse your software license keys with SAP licensing of the usage of named users. These are two different things! Usage by users of an SAP instance will be monitored by your auditing team, and normally the only function of the Basis group in this regard is using su01 to register the "type" of each user. 

Now there is only one other really important number you need to know: the phone number for your Basis technical consultant!