Electrons are negatively charged subatomic particle that can either be bound to the nucleus of an atom where they orbit in certain ‘shells’ with a number of electrons, (so that the total negative charge equals the total positive charge of the protons/positively charged particles in the nucleus and the atom overall is neutral), or exist in free space or as part of a plasma. We use the charge of one electron as part of the definition for electrical charge as electrons are often thought as responsible for the flow of electricity in conductive materials. Electrons can also be one of the things that bonds atoms to one another either through sharing, (covalent bonds), or swapping, (ionic). They are very small, with a mass much smaller than the other atomic particles. I hope this helps and let me know if you have any more questions!
Hollie has given you a very complete description of an electron which I think answers your question exactly. Your question did get me thinking about related matters and about one of my science heros a man called Paul Dirac. Dirac created an equation know now as the Dirac equation which describes the behaviour of sub atomic particles in a very exact way – one which is the electron. Another scientist looked at the Dirac equation and said if that equation is correct then something up until then never thought of, anti-matter, must also exist. Some years later anti-matter was proved to exist. The thing about anti-matter is that if it comes into contact with matter (that’s the stuff you and I and everything around us is made of) the two destroy each other. Thankfully there is very little anti-matter in the universe so we are safe. The Dirac equation is considered such an important contribution to science that it is carved in stone in Westminster Abbey.