Newbie alert.. NEED YOUR ANSWERS

So im new to the cryptocurrency world and was introduced by my previous manager and before I start trading I've been doing some research, reading etc but nothing answered my question about spot trading.. yes theres alot of information out there but I dont seem to find the answer to my question .. hence why am here..so in Binance spot trading do you sell all or just your profit? (For example you bought a coin for 15$ and you gain a profit of 3.5$, do you sell all i.e 18.5$ or do you sell only the 3.5$ profit)..