Start off by moving forward. You will reach a first hole in a short while (#1). Don't even think about using your whip here. You will have to make a successful jump. This is quite challenging, so you might consider saving your game first. There's also a second hole here. Thankfully, it's easier to avoid. You will reach a new location very soon (#2). Don't worry, we'll find a way to get to the other side.
Turn left. You will have to use a gun or a whip here. Aim at the small wooden object (it's a small stone; #1). You should also take a few steps back, so you don't get hit by anything. You may proceed to the new passageway (#2).
There's a much larger bridge here (#1). You will have to use it to get to the other side of the tracks. Turn left and jump down to one of the lower platforms (#2). You will have to find a cover by a small group of crates. There are also a few interesting objects here. Listen to what the Billy has to say before you decide to pick them up.
You probably thought that waiting for the train would do the trick. Sadly, you won't be able to choose this strategy. The only way to finish up with this mission would be to kill ALL enemy units. Only then you'll be able to proceed to the next chapter of the campaign mode. Start off by picking up a shotgun (#1). There's also a lot of ammunition here. I would recommend that you start using your newly acquired weapon. It's quite powerful, so you won't have any major problems with most of the bandits. Lean out carefully and kill some of the visible enemies (#2).
Keep shooting at the bad guys. They will be leaving a nearby mine, so you won't have to worry that they'll surprise you. If you're lucky, you should also be able to blow up a nearby building (#1). This would help to kill a few additional bandits. More of them will arrive here shortly (#2). Make sure that you save your progress frequently, as it is very likely that you'll be hit (more than once).
Bear in mind that you have a limited ammo supply for the shotgun. Thankfully, you can also use the revolver (#1). The only difference is that you'll have to aim at heads of your opponents. An interesting cut-scene will appear on your screen in just a few seconds (#2). You will see Ray as he is exiting the mine (#2). Thankfully, you won't have to fight him here. Billy will use the train to escape. This is the end of this chapter.