Accounting is maintained at double entry systems.
As per double entry system, there is always two effects or two accounts are involved in each transactions.
Rozy purchase car by cheque. In this transaction, bank account is reduced and car which is asset is increased. In this transaction, two accounts are involved. Bank and Car.
Xen has paid cash to Lara. In this transaction, cash is reduced and Lara which is our creditor is also reduced. There are two accounts involved in this transaction. Lara and Cash.
Share purchased in XYZ ltd. In this transaction, two accounts are involved bank and Shares in XYZ ltd. Investment account (Shares in XYZ ltd) is increased and Bank account is reduced.
I hope now you are able to understand what double entry system is. We can use this system to do journal entry or posting in ledgers.