I am using "me98"(archive) to delete a PO that have a mistake for vendor code. 
The following step is: 
the 1 step: I maintained and saved a variant.  For this variant, I have to create a name for this variant and select the PO which want to delete. it's right? 
the 2 step: I maintained a "Start Date".  For "Start Date",I select the "immediate " to execute it.  Is it right? 
the 3 step: whether I maintained the "Spool Params" or not?  May I execute it immediately or not? 
I have no idea for deleting PO via the "archive".   How can i do that ? 

Archiving is not deleting. What do you think why SAP developed that much programs to retrieve and read data from an archive. 

Archiving is saving and keeping data for a certain period (based on local laws for data retention and auditing purposes) outside of the production data base.  Such a job is usually done to keep the database small and fast. 

While doing archiving the records are written to a file and verified to be readable and then the original record gets deleted from the database. Only if you delete then the file with the archived data you have deleted the record forever. 

Sometimes people seems to work like a burglar and want erase every single evidence for an error. But even errors, or especially errors are subject to be audited if they are corrected in the right way. This is the same for financial and tax auditiors as for auditors for ISO 9000. 

To be able to archive, you need to setup the path from SAP to the archive. You need to define the size of your archive and how may records should be kept there. 

Step 1: Create variant for Archiving. Give it a name. Enter your PO number. Flag One step procedure. Flag detailed log. Erase flag for test run. 

Step 2: Maintain your start date, you can use Immediate in such a small case. 

Step 3: Maintain spool parameters. Enter your printer and set the values if you want to print immediatly and if you want keep the print. I suggest to hold the spool in the system. This helps you to determine any error. 

Step 4. Execute the variant. 

It creates 4 jobs: 

ARV_MM_EKKO_SUB...., ARV_MM_EKKO_WRI.... ARV_MM_EKKO_DEL..... 
ARV_MM_EKKO_STO.... If one of the steps fails, then everything is rolled back, hence nothing is archived, the record is still in your database. In this case use the jobs spool and joblogs to find out what happend.

Related links:
How to Archive the Material Master?
Archiving a Material Master Record

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