We are looking at the difference between elements, compounds, and mixtures. Elements are the purest form of a chemical substance and are composed of only one type of atom. In other words, all of the atoms in an element will have the same number of protons. Please note that a chemical composed of two or more of the same type of element (H2, O2, etc.) are also considered elemental forms as well.
A chemical compound is a chemical that is composed of at least two different types of elements. These elements are combined together in fixed proportions and structures to produce a single type of unique particle. Like an element, a compound is considered a pure substance (meaning there is only one type of particle in the substance).
A mixture is a combination of two or more different chemical compounds or elemental substances. It is not a pure substance, but a combination multiple particles. It can be separated into different type of particles. There are two different types of mixtures, homogeneous and heterogeneous. In heterogeneous mixtures, you can see the two different types of substances with your eye. In homogeneous mixtures, you cannot see the two different substances (they appear as a single phase to the eye).