I personally use a spreadsheet but I'm sure there are better way to do it.
Do you know any good websites/apps to do it?
I think you not needed a spreadsheet or anything else because in trading yes we make profit and losses but it is more on winning or profit if you use to trade well or lets we say that you have a good skills in trading we doesn't need it anymore it will just ruin your trade by being greedy if you lose more than profit in some circumstances.
I haven't think about it by yes for starters a spreadsheet would be a good thing to used for tracking your win/loss record. However, right now I haven't used any because I don't take profit but instead try to roll my money on investing or just simple don't trade if I don't feel like to. But its a good thing that you brought this idea. I don't know if there is a software out there that can you get to automatically jot this information for you. If there is one, it would be a great tool for us traders.