FGI1 to create report / FGI4 to create form

Hi,

really need advice on creating report/form.

1) may i know why need to have both form FGI4 and report FGI1?

2) when create report FGI1, what is the difference that the report with form and copy from report? i mean if i create report with form, what is the purpose and if i create a report copy from standard report, what is the purpose.

i know if create with both form and report cannot. i just want to know what is the difference.

3) i want to add column cost center in the report. which method in point 2 above i should follow?

thanks

rgds