Please its not tutorial Forum stop post every steps try to read something stop post everything you are doing you don't know anything about ASM and you trying to create one you don't know how to change parameter and you try before reading its not just step to apply you have to know what you do
READ ORACLE DOCUMENTATION
alter system set DB_RECOVERY_FILE_DEST='+DATA' scope=both;
You don't seem to have a value for the asm_diskstring parameter in your ASM init.ora file at the first place.
Please put the correct value for that parameter where your disks can be discovered, then start the ASM instance and try to create the diskgroups.