It is nice if you add all your accounts and instruments to the ledger at the beginning. It can be challenging but you have to fill up your ledger with initial data only once. (On the other hand you can ignore an account and add it later.)
The video said that most internet bank can only tell the actual balance and not the balance for a given time. It is true but you can calculate the balance for a given time with the help of your transaction history. If today is August 3 and my balance is 1000 USD and in this month I had only two spending 6 and 8 USD then my balance was 1014 at August 1.
If you need some idea how to tell the current value of your flat then see this page.