I have played the first part of the Injun's world 3 or 4 times now, but I always get stuck when I have to make a torch. I've tried combining the spear with the resin and the fishing rod to the resin, but it doesn't work. The walkthrough says that I should have all the ingredients to make a torch, but I can't seem to do it. What am I doing wrong?

You must not use the spear, but combine a material and resin to make your torch. Then, of course, you have to burn it.

I've tried combining everything in my inventory with the resin. The only thing that combines is Oscar's shorts, but when I try to place this in the campfire, nothing happens! What am I doing wrong?

You're trying to place the right thing in the wrong place
Try again in the entry of the cave