I have a Member Object, donation fund object, and donation line object.

Member name: Sam
Donation Fund name: Office computers
Donation Fund name: Surplus
Donation line item Amount: $100

If Member "Sam" Donates $100 to donation fund "Office Computers", and the remaining needed to cover the goal of that fund is only $50, how Do I transfer the remainig $50 to donation fund Surplus? 

Once the transfer is made I want a record of where the surplus got its donation from.

Can someone please help me create a calendar date converter.
I need a user to enter a date on the gregorian, and then hit enter to convert that date on the lunar calendar.

Im new to coding and apex so please be detailed on this one. TY.

When creating a line item, i have 3 Relationship fields.
1) Member lookup
2) Line item MD relationship (to the type of line item im creating.) (Donation to the donation fund its related to)
3) MD relation to an invoice.

1)Any donation a user enters should be added to a member. 2) It should be added to the donation fund. 3) it should be added to the members invoice.
If theres an Invoice with the selected members name and a statusof OPEN it should be added to that invoice, if not a invoice with that name should be created.

Either some help with the criteria i gave, or any better suggestions would be greatly appreciated.
TY 

I never wrote any apex code so any help you give me, please make it very detailed so I can follow along.
TY

I have a Member Object, donation fund object, and donation line object.

Member name: Sam
Donation Fund name: Office computers
Donation Fund name: Surplus
Donation line item Amount: $100

If Member "Sam" Donates $100 to donation fund "Office Computers", and the remaining needed to cover the goal of that fund is only $50, how Do I transfer the remainig $50 to donation fund Surplus? 

Once the transfer is made I want a record of where the surplus got its donation from.

Can someone please help me create a calendar date converter.
I need a user to enter a date on the gregorian, and then hit enter to convert that date on the lunar calendar.

Im new to coding and apex so please be detailed on this one. TY.