What are atoms?

Atoms are small particles that make up everything.  If you picture an object made up from mini-footballs then that's what the atoms look like that make up the object just on a much, much smaller scale.

Atoms have protons (positive charges) , Electrons (negative charges) and Neutrons (neutral charges) in them.  It depends on the atom as to how many of each you have. Standard atoms make up the periodic table and are called elements.  Elements are atoms in their most basic form and it's from these elements that everything is made-up from.