Ledger Balance means Trade date Balance
Available Balance means Settlement date Balance
Trade date + 2 workings days = Settlement date
For expample, if you buy 400 shs of HSBC in Day 1
then in day 1 your ledger balance have 400 shs of HSBC. and available for sale is zero
In day 2, Your leger balance & available for sale is 400 shs of HSBC