Hello,
Availability check 01 , 02 work in combination with Checking Rule that is nothing but the scope of check defined in OVZ9. Here you can define what should be include or exclude from ATP check like current stock, inward movements and outward movements of the material.planned goods receipts against PR, PO, PIR, , safety stock etc.
In OVZ2 you can define the ATP check control like 01 and 02 you an define the summation to individual requirements.
The flag ' With reqmts.quants' in only relevant when the accumulation in transaction OVZ2 is set to the value '2' or '3'. Please consider the F1-help for the field 'Accumul' in transaction OVZ2 in order to understand kow accumulation works.
Please refer these useful documents,
General Documentation - Supply Chain Management (SCM) - SCN Wiki
General Customizing Settings of the Availability Check - ERP SD - SCN Wiki
Best Regards,
R.Brahmankar