How do you adjust Shimano gears on a mountain bike?

To adjust Shimano gears on a mountain bike, start by shifting to the smallest chainring and cog. Then, use the barrel adjuster to fine-tune the shifting. If the chain is not shifting smoothly, adjust the cable tension by turning the barrel adjuster. Test the gears by shifting through all the gears to ensure smooth operation. If needed, repeat the process until the gears shift smoothly.