How can i apply the discount in my invoices?

You can apply the discount in your voucher in two ways
For voucher level you can apply discount in bill sundry
and for item level discount you can use item wise discount
To apply the discount through bill sundry please follow these steps:
Step 1: Go to transactions menu
Step 2: Then create or modify the invoice such as sale,purchase in which you want to apply the discount
Step 3: Then After creating the invoice apply the discount in bill sundry 
Step 4: If discount bill sundry is not found you can create it by pressing f3 key in the bill sundry grid
To apply the discount at item level please follow these steps:
Step 1: Go to administration menu
Step 2: Then click on configuration button
Step 3: Then click on features and option
Step 4: Then click on inventory tab
Step 5: Then select item-wise discount type as simple or compound as required
Step 6: Then save the changes
Step 7: Then go to administration menu again
Step 8: Then click on configuration
Step 9: Then click on voucher series configuration
Step 10: Then select the voucher such as sale,purchase etc after that select the series
Step 11: Then click on voucher configuration and enable item wise discount
Step 12: Afterwards specify the discount structure as required and save the changes
Step 13: Then go to transaction menu and open the invoice in which you want to apply the discount 
Step 14: Afterwards while creating the invoice whenever you will press enter in item grid it will give you a prompt to apply the discount as per the structure defined by you."