A friend of mine wants to use a Proxy on his home computer because his parents have blocked many games and social media services. My question is, if he is using a Proxy, will his parents be able to see that he is using a Proxy?
If your friend is using a proxy, all the requests will look as requests towards the IP of the proxy. Depending on your friend's parents' knowledge of networks, they might find that as a suspicious behavior. In normal cases where the average parents don't know much about proxies, there should not be any problem.