You use the IC General Journal to post intercompany transactions. An intercompany journal is a type of general journal, so you can use it to post transactions to G/L, bank, customer, vendor and fixed assets accounts. However, to create an intercompany transaction, the journal line must contain either an IC partner account or a customer or vendor account that has been assigned an intercompany partner code.
The lines in the window can be outgoing intercompany lines that you set up or incoming lines that you accepted in your inbox.