@859frcc45 Surely antimatter and matter would annihilate each other and we wouldn’t have any stuff at all, just radiation ?! But experiments have shown that particles are more likely to change from their antiparticle to the normal particle than the other way round – and this is why we only observe normal particles in real life. As for dark matter – who knows. Nobody can see it. Possibly weakly interacting particles that don’t radiate much energy and therefore are not observed.
Dark matter is just stuff out in space we can’t see, because it doesn’t reflect starlight so it’s dark and we can’t see it!
We’re not sure why there’s more matter than antimatter, but as Lidunka says it looks like particles just prefer to be regular particles than antiparticles. Experiments and theory both agree with this, but the fundamental reason why isn’t known yet.