Most of the colliders in particle physics are based on the Theory of Relativity (E=mc2) This tells us that mass and energy are interchangeable. That simply means that we can convert energy into mass and mass into energy, this can be done by a collision. To give you a very simple example, lets imagine we plug two apples into the Large Hadron Collider LHC (the keyword here is imagine because it is not really possible 😉 ) we make them go really fast to almost the speed of light. After they reach this speed where they can turn around the 27km long LHC 11,000 times a second we let them smash against each other. When these two apples smash they suddenly create a watermelon! and that watermelon then decays into thousands of raisins!
This is very similar to what we actually do with particles. When we collide protons (proton are made of quarks) they produce things like electrons along with many other particles. This is simply because energy has converted into mass. We don’t really want to see these electrons because we know they exist we are actually aiming to see something we have never seen before like the Higgs boson for example.