Is my anonymity ensured when using a VPN ?

It is recommended to assume that nothing remains 100% anonymous on the Internet.  When you use a good VPN it ensures that your online activity remains under camouflage. For example you might actually be browsing from the UK but it will seem you are surfing from Australia.
That is why it is very important to read the reviews of the different VPN providers to learn about their different protocols and how different protocols monitor your online activity.