If you've hit all three green buttons thus far, the last one will be right in front of that gate that you can hit to unlock it! You'll find the gold bolt there shortly after. Then, a little after, you'll find another railing to the right, as seen in the above right picture. It will lead to a section with two more green buttons that we can hit, then you can jump back onto the main railing. After hitting this green button in the above picture, immediately jump onto the railing that will be coming up on the right. When you see the green button in the left picture above, it means you're getting close to the very first gold bolt in the planet! When you hit that green button, you'll have to hit three more green buttons in order to open the path to the gold bolt, but it should be fairly simple. If you can manage to do that, the actual grindrail part of the level should be easy for you. Basically, what you'll need to do is move inbetween incoming traffic by jumping along different rails. The grindrails are very similar to all the other ones we've encountered thus far, jumping over electricity and other blocks as well as jumping over or knocking away bombs, but also introduces an interesting mechanic of having cars move in your direction as you ride along several rails. Take care of them and then ride on the grindrail that should be there. Up at the top of the area after the elevator, there will be two Blarg soldiers. For now, head in the other direction and you'll find an elevator. In the middle of the room you should find a giant bolt that you can crank, go ahead and do that and it will raise a bridge down the path we will be going down later. It even has another Gadgetron Vendor, just in case you missed the first one on the planet. Press the green button on the left side of it and you'll gain access to a room we'll be in a few times. You should eventually find yourself in front of an orange forcefield.
For an easy way to kill these guys, just snipe them from a distance with the Plasma Striker. When you look at what's inside, you'll find the newest and last weapon you can purchase from the vendors, the Sheepinator! Once you've done that, head down the path and you should find some Blarg soldiers along the way. When you first get onto the planet, you should find a Gadgetron Vendor near your ship.