Henry Reich, from Minute Physics, explains what antimatter is and it is the same as matter, but with opposite electrical charges. The issue is that antimatter is hard to come by or to store as any contact between matter and antimatter will lead to annihilation of both and then a lot of energy is released.
How do you obtain antimatter? You need to use something like CERN’s to hit particles against each other so hard that some antimatter is also created. To obtain antimatter you need to excite the vacuum to obtain a matter-antimatter pair and then steal one of the two for your experiments. Much like the Casimir effect or like the Hawking radiation would work.