I have already talked in depth about what 'going unconditional' means in Step 7 of this website so I am not going to repeat myself; however, for completeness I will note that you will need to get your conveyancer to communicate once the building and pest condition is satisfied and once your mortgage broker has confirmed that you have finance.
Once this is done, the contract will be considered unconditional and both parties are legally locked into the contract.
However, there are circumstances where you may need more time to satisfy a condition - in which case you need to request an extension otherwise the period for you to satisfy the condition will lapse and the contract will then become unconditional in any event.
Requesting extensions to conditions
Extension requests, in my experience, are usually made in connection with the finance clause rather than the building and pest inspection clause (unless there is a major defect the parties are working through). Generally speaking, Sellers are not obliged to accept your extension request - but if it is due to things such as delays with the bank then I have found most sellers are usually receptive to this. However, you shouldn’t rely on the sellers giving you an extension - always try to satisfy the finance condition within the negotiated period.
If you do need an extension, you need to work with your mortgage broker to figure out what is an appropriate extension period for the finance clause and then get your conveyancer to communicate this accordingly.
You also need to discuss the consequences of not getting the extension with your conveyancer - whether you need to try pull the plug on the deal by saying you couldn’t get finance or if you are confident you will get finance before settlement in any event and therefore happy to let the contract go unconditional. Remember that the consequences could differ depending on the state and terms of your contract - so you need to rely on your conveyancer in these situations.