This is the first important principle to understand. The word matter includes almost everything. If we were able to take a piece of matter such as a drop of water, divided it by two and kept dividing by two until it couldn't be divided any further whileit was still water we would eventually have a molecule of water. An atom is also divisible - into protons and electrons. Both are electrical particles and neither is divisible.
Electrons are the smallest and lightest and are said to be negatively charged.
Protons on the other hand are about 1800 times the mass of electrons and are positively charged. In theory, negative lines of force will not join other negative lines of force. In fact they tend to repel each other. Similarly positive lines of force act in the same way. Like forces repel and unlike forces attract .