Hi Lanai,
In Business Central you link the bank account to a Posting Group which holds the GL code which is updated when you post to the bank account. (G/L entries will be posted against the GL code and Bank Account Ledger Entries will be posted against the bank account)
For example in by demo company this bank account is linked to a Posting Group called "CHECKING".

If I look at the Posting Group you can see this is linked to a GL code 40100

Which is in turn shown in the Chart of Accounts:

** Please note you won't be able to post to the bank account until its been linked to a GL code.
As mentioned above when I post to this bank account G/L entries will be created against this GL code and bank account ledger entries against the bank account.
Hope this helps
Thanks
Gavin