How can I adjust the derailleur on my bike?

To adjust the derailleur on your bike, start by shifting to the smallest chainring and cog. Use the barrel adjuster to fine-tune the alignment of the derailleur. Make sure the chain is running smoothly and doesn't rub against the derailleur. Test the gears by shifting through them to ensure smooth operation. If needed, make further adjustments until the gears shift smoothly.