Career in Trading

I don't think of physical commodity trading when people talk about "trading" in the way you have described (I.e S&T at a bank or commodities trading); I think of commodities as a group/subset within an umbrella group of Sell-Side Trading & Buy-Side/Prop Trading more likely.

Still agree that OP should look up the difference between the more client-facing S&T-esque trader and the less franchise-focused Prop Trader. Although traders in S&T (depending on the group) can warehouse risk and take on certain prop views under the guise of "pre-hedging," the primary day-to-day in S&T is much different than prop trading.

The biggest difference in S&T would be the day-to-day tasks heavily focusing on client-centric related objectives: I.e., pricing and executing trades, hedging and managing risk that you're warehousing, and thinking about ideas to pitch to clients. In Prop Trading, day-to-day tasks heavily focus on strategy generation/backtesting, hedging, managing positions you're warehousing, and automating important tasks on the desk. Prop Trading emphasizes alpha generation/strategy since you do not rely on franchise flow to take on positions. 

I have been in both S&T and Prop now, and the autonomy, tie to P/L, and responsibilities are much more discretionary and dependent on the individual at a prop trading firm. Within S&T, it's a well-oiled machine that services clients and manages risk. Within prop trading, there are several small teams of a few people who specialize in certain product strategies and are competing against other firms. The payout is heavily dependent on individual contribution/team performance. This is all very generic; within certain bank groups, the role can be very similar.