BADI modify and change

go to SE24 --> CL_EX_FI_TRANS_DATE_DERIVE

i can double click on the method name.it lead me to the code where i can write my piece of code

method

.

*--- write code my piece of code

.

endmethod

got to SE18 -->FI_TRANS_DATE_DERIVE

when i double click on the method name nothing happen. It there a button i must click to get

method

...

endmethod

Is this two method the only way to search for and modify a badi

Can anyone explain to me what if i want to create a badi? how will the transaction let recognise the badi?

what good tips is there to know about BADI