Anyway, manual is here.
ASM has been integrated to Grid Infrastructure.
In 11.2, ASM is part of the Grid Infrastructure install. And GI must be installed in a dedicated ORACLE_HOME before installing the RDBMS in a separate ORACLE_HOME.
If you server only has the RDBMS installed, you'd need to check with Oracle Support as to how you can install GI and configure ASM (and then migrate your database datafiles from filesystem to ASM).
If you are planning to go to ASM on a separate server, remember that you must install GI with ASM first. Therefore, the underlying disk volumes / LUNs must be assigned and available before you run ASMCA (ASM Configuration Assistant) as part of the ASM install.
After getting the storage team to allocate the required LUNs, you can run asmca from the Grid Infrastructure install.
(Note : In my experience, the default behaviour during GI is to also run ASMCA immediately to configure the ASM DiskGroups. If this hadn't been done earlier, you'd have to do it now).
Please see the oracle documentation from http://docs.oracle.com. I suggest you practice creating disk groups on a test server and storage.