The first 14 to 16 weeks of your puppy's life is when they will be most open to new experiences and is often referred to as the 'socialisation window'. Socialising your puppy involves exposing them to lots of different environments, things, people and animals in a positive and safe way to help them have the best chance of being well adjusted canine citizens.
As this window coincides with the period of time in which your puppy may not have full protection from their vaccinations, it's crucial to choose the location of any socialisation very wisely. This is particularly important for avoiding parvovirus, which still kills plenty of puppies in Australia every year.
If you have friends or family members with healthy, fully vaccinated, well socialised dogs you could also ask them to come around for a puppy playdate. Just be sure to keep an eye on things to make sure the play doesn't get out of hand. Puppies learn their social skills by 14 weeks of age therefore it is important to be involved and help learn the appropriate way to interact with other dogs and humans.
You can take your puppy out in public if necessary, however, you should always carry them and not let them on the ground, nor come in contact with unknown dogs before they have finished their full course of puppy vaccinations.