Explain the relationship between elements and atoms.

The relationship between elements and atoms is really quite simple: elements are made up of atoms.
More specifically, elements are made up of only one type of atom.
The element hydrogen, for example, is made up of only hydrogen atoms. Oxygen is made up of only oxygen atoms. Einsteinium (yes, there is such an element), is made up of only einsteinium atoms. And so on.
Currently, there are 118 elements on the periodic table of elements, which is that big chart with rows of colored squares with different letters and numbers that you see hanging on the wall in the science room.
The first 94 elements on the periodic table occur in nature, although some of the elements are found only in very, very small amounts. Elements like gold, silver, copper, sulfur, and carbon have been known for centuries. Other elements in the periodic table, such as einsteinium (which you already know about), seaborgium, and ununquadium (who makes up these names?), have only been synthesized (artificially created) in laboratories by mad scientists or in nuclear reactors, and some of those elements were added to the periodic table as recently as 2016.
"Great," you say. "So what's an atom?" An atom is the smallest unit of ordinary matter. In other words, an atom is the smallest thing that we put a finger on, if we had fingers small enough to touch an atom.
There are things smaller than atoms called "elementary particles," like quarks, leptons, and bosons, but good luck finding one or putting a finger on it.
Back to atoms: atoms are composed of protons, electrons, and neutrons. Protons carry a positive electrical charge and live in the nucleus (more or less the middle) of the atom. Neutrons carry no electrical charge and live with the protons in the nucleus of the atom. Electrons carry a negative electrical charge and orbit (fly around) the nucleus.
All atoms have protons and electrons. All atoms except hydrogen have neutrons. Hydrogen apparently didn't feel the need for any neutrons.
The type of atom is determined by the number of protons, neutrons, and electrons it has. As you already know, all hydrogen atoms have 1 proton, 1 electron, and zero neutrons. All oxygen atoms have 8 protons, 8 neutrons, and 8 electrons. All einsteinium atoms have 99 protons, 153 neutrons, and 99 electrons. By the way, einsteinium has no known uses, or at least none that we've discovered so far.
In summary, elements are made up of one type of atom. Atoms, the smallest unit of ordinary matter, are made up of protons, neutrons (except hydrogen), and electrons.