In simple terms, our planet is just a big ball of very hot stuff which, at the surface where it is exposed to space, has cooled to form crystalline solids (igneous rocks) composed of minerals. Minerals in turn are combinations of elements, which are made of smaller particles, which are made of smaller particles, which are made of..... who knows what.
To be classified as a mineral, a substance must be an inorganic, naturally formed solid, with a specific chemical formula and a fixed internal structure. For example, coal is not a mineral (it's organic), but snow meets all five (5) requirements and therefore is a mineral.
Study the Physical properties of it:
Luster: The quantity and quality of light reflected from the surface. Most identification schemes begin with a simple classification based on luster. Because of this, luster is the first fundamental test to be made when identifying any mineral.
Metallic: looks like a metal. Metallic minerals are commonly shiny and opaque
Non-metallic: doesn't look like a metal.
Color: Obvious, but not always definitive. Sulfur is (almost) always yellow, and there are a few others, but not many minerals have a fixed color. Small amounts of impurities can drastically change a mineral's color.
Streak: The color of the powdered mineral. The test is usually performed by scraping the mineral across a piece of unglazed porcelain. Streak can be definitive. Good examples include hematite (always red-brown no matter what form it's in) and chromite (distinguished from the hundreds of other black minerals by its chocolate-brown streak).
Hardness: Hardness is the resistance of a mineral to scratching. It does NOT refer to how easily the mineral is broken. Hardness is a measure of the bonding strength between atoms. If these bonds are strong, the mineral is not easily scratched. Minerals with weaker bonds are more easily scratched.
Fracture: The mineral just breaks, leaving an uneven surface. Most are irregular but there are some special cases (ex: the conchoidal fractures common to quartz and glass)
Cleavage: The mineral splits along closely spaces parallel planes, leaving a mirror surface which will flash at you if rotated in the light.Controlled by crystalline structure and chemical bonding.
0, 1, 2, 3, 4, and 6 cleavage planes can exist. Most difficult physical property for students to understand and identify.
Specific Gravity: Defined as "the weight of a specific volume of a mineral divided by the weight of an equal volume of water (at 4°C.)" Since water is always 1.0, it's the same number as density without any units (they cancel). This is almost impossible to measure in the field, but a rough approximation and be determined.
Magnetism: Magnetite is naturally magnetic.
Taste: Some minerals have a distinctive taste. Notable examples include Halite (rock salt), and Chalcanthite (a copper sulfate - be careful with this one!!). I don't generally recommend the taste test.
Smell: Some minerals have a distinctive odor. Sulfur is a good example.