If we're talking about selling a friend your bitcoin, it's completely fine, just remember that a friend can also steal from you and stop being a friend, but the money will be gone.
Make sure you check if the money is real and secured before you send him BTC.
If we're talking about your friend helping you trade your BTC, I think that you shouldn't do it. It's an easy task and you can do everything yourself. Don't let others between you and your money.
Before making a transaction with a friend, we must ask what they want. We can also make sure we have Bitcoin and he also has his money. If everything is clear, then we can make transactions with friends.
The best step is to invest in bitcoin independently, even if you don't understand or don't know how it works but really want to invest in bitcoin, it's better to learn first. And it would be even better if your friends understand how to invest in Bitcoin. Learn with him instead of trusting to trade your bitcoins to your best friend. Apart from that, entrusting your trading to your own friends carries a high risk, you could lose your friend if he makes the wrong investment decision, causing you to suffer a loss.
By teaching our friend to buy Bitcoin on the exchange, we can at least open his mind to the possibility of buying his Bitcoin directly on the exchange without us needing to know. He can learn investing or trading after we explain more to him.