You can set the source of the yeast bomb by control left clicking somewhere in the world. Then you can place the yeast bomb next to the tungsten vein and when you place an item at the source of the yeast bomb, it explodes. You can think of the source as a trigger point for the bomb. The bomb reacts to items and to other logic components at the trigger point.
Yeah you hold the bomb in your hand while setting the source, and then after you've set the source, you place the bomb as a structure by right clicking. All structures that require a source or a target work like this, so things like the logic gates. The bomb can also be put inside the press to automatically detonate it.
I don't have the capacity at the moment to make a full tutorial of the game, but if someone wants to take that task upon themselves, go for it.