• FI – AP = Account Payable
• FI – AR = Account Recievable
• FI – GL = General Ledger
• FI – AA = Asset Acounting

Out of above 4 modules, FI-AP closely connects with MM and FI-AR with SD .

• SD = Sales and Distribution
• MM = Material Management

These 2 modules are core of business.

From accounting percepective, the importance of these 2 is revenue regonises at shipping timing and payable recognise through inspection, strictly speaking 3 way matching as standard way in SAP world.