So as we know the cash rate changes daily in the cash market, this is known as the 'actual' cash rate. So what the RBA does to meet the 'target' cash rate (currently 2.5) is to decrease the volume (liquidity) of money in the cash market, this is a case where there is a large volume of cash in the market and the 'actual' cash rate is lower than target rate. The following happens to increase the cash rate:
The RBA increases the cash rate by reducing the liquidity (volume) of cash in the cash market through ‘open market operations’. It does this by enticing banks to give money to the RBA. The RBA sells Commonwealth Government Securities (CGS) or Repurchase Agreements (REPOS) to the banks in exchange for cash. This reduces the volume of cash that banks can lend or borrow between themselves in their Exchange Settlement Accounts (ESAs) thus forcing the cash lending rate between banks to increase.
Hope this helps.