How can I know if something is a sin?
The first thing we should do as believers if we are not certain about an action that could be a sin, is to dive into Scripture. God gave us the Bible as a tool and manual to get through life and live it out the way He intended us to. It is also never a bad idea to consult a fellow believer. Friends and family can be useful but any kind of pastor or any kind of Christian leader would be the best option here. The Holy Spirit can also help guide us and convict us of sins. The Holy Spirit really acts like your conscience and is primarily used in that way when someone becomes a Christian. John 14:17 “even the Spirit of truth, whom the world cannot receive, because it neither sees him or nor knows him. You know him, for he dwells with you and will be in you”