how to transfer a form details to another form?

tableA.Field1 := tableB.Field1;
tableA.Field2 := tableB.Field2;
...and so on.

Skip fields which do not match.

Wrap the code in a function so you can reuse it. Even if you don't plan to re-use it still wrap it in a separate function - it will make your code more readable,

There is not much philosophy or science there. It is just a series of assigment statements wrapped in a function, nothing more.

When you call ToRecord.TRANSFERFIELDS(FromRecord) the system copies fields from FromRecord to ToRecord. The idea is to build a function doing the almost the same but skipping unwanted fields. Since the TRANSFERFIELDS is called on a destination record (ToRecord.REANSFERFIELDS...) then to make my custom copy fields function similar I am also defining it on source table.

I am also trying to stick to specific naming convention, and call my function CopyFromSomeRec() so furtehr down the code I can clearly see what it is doing
ToRecord.CopyFromRecordA(RecordA)

If the function is suposed to copy fields from some record A to record B, then on table B (destination table) I would create function CopyFromRecordA, with RecordA as a parameter, and inside this function put a series of assignments.

Just note that both TRANSFERFIELDS and a function assigning field values is not supposed to insert anyting into the database. Both are supposed to do in-memory copy - that's it. If you want to make a copy of record A into record B in the database you need to insert that copy into the DB

RecB.CopyFromRecordA(RecA);
RecB.INSERT;