We are moving to Melbourne from London with 5 years old son,love to know about the schooling ?

Melbourne has a mix (as does Australia really) of public (government funded schooling) and private (you pay and some area expensive and others are very expensive ie <$10k and >$10k). Public schools vary a great deal from fantastic to unfortunately embattled so it really depends on where you live as to where you are likely to be able to go. Public schools must provide a place for your child if you are within their designated zone as I understand it. If you want to go to a public school that you are not zoned for you can but it's up to them whether they take you are not (class sizes etc). Some of the fantastic public schools don't take kids outside of their zone because they have reached their limits and people pay extra money to buy a house in the area eg Balwyn High, McKinnon High.
Private schools... there is the Catholic system which is, dependant upon the school, in the <$10k category and you really need to contact them to have them give you fees, ethos and their differentiators. These are spread all over Melbourne. The other group of Private schools are 'independent' but align in two main groups (ASG and forgot the other one!). Their fees are much higher and most are in the Eastern Suburbs with others spread throughout Melbourne (Essendon, Brighton, etc). It's not an easy question to answer so perhaps refer to the Victorian Government website/Education Department website for information. Also I presume there is a website for Independent Schools system and the Catholic school system.