Before creating Account Alias account field in a form is looks like the following
Now to create Account Alias following setups are required.
First of all set the profile option 'Flexfields:Shorthand Entry' as 'All Entries'.
Then select Aliases under key flex field menu. Query the accounting structure. Max size is 20. Give a Prompt name. Now give the Alias Name, Account combination, Description, Effective from as below.
Now save the record and it will be compiled automatically.
Now query the Account structure again from Key flexfield Segments and Compile it again.
Set up Part ends here.To check the effect you can select any account field in a form like below. Select the alias name then click on OK.