Question on taxes and ETF

Im new to investing and despite trying to read more about it, I still have many questions. I am using a robo-advisor which implies I transfer money to a UK account (Im portuguese btw). Lets say I have a 1000 euros portfolio and in 5 years its worth 1200 euros. What happens when I want to withdraw all the money, mostly regarding taxes? I have to pay taxes on the 200 euros net gain? On all the 1200 euros? Sorry if it is a stupid question..