I am playing Ocarina of Time (the 3DS version) for the first time, and I am at the part where I need to enter Dodongo's Cave. I can carry Bomb Flowers, but when I try to take them to the boulder blocking off the entrance, they explode before I can even come near. I noticed a section of the wall that might be bombable, but I can't get the bomb to there without having it explode either, even though it's not that far away. Maybe I'm just not fast enough. I looked up a walkthrough, and it said to throw the Bomb Flower over the fence. The game wouldn't let me do that when I tried; even when I got really close to the fence, the bomb somehow bounced off of nothing and went the other way. What am I doing wrong?
You do have to throw a bomb flower over a fence; most likely, you are trying from the wrong place.
You aren't just trying to get it from anywhere that looks like it might work; there is a specific place you need to go to as part of the main quest/story/mission in order to open the cavern. It is high above the cavern entrance; you throw a bomb flower way down from above.
You can get to this spot by continuing to follow Death Mountain Trail up. The space should be somewhat obvious when you see it; there is a bomb flower in a very specific space directly high above the Cavern entrance.
You can see the space you need to be near the start of this video, at 0:40:.