How are metalloids different from metals?
Metalloids have properties in between those of the metals and non-metals and are semiconductors (whereas metals are conductors and nonmetals are not conductors) and used extensively in circuitry (like computer chips).
They are all solids at room temperature, not quite as malleable as metals....but not quite as brittle as nonmetals. They can be shiny (have luster) or not whereas all metal are shiny.
Although we typically think of there being a very black and white distinction between shiny, conductive metals and brittle, non-conductive (or even non-solid) non-metals in reall life there is not always such a sharp distinction. As you move from left to right across a row on the Periodic Table, elements gradually become more non-metallic in their properties. The staircase serves to indicate a cut-off point where the non-metallic properties are greater than the metallic properties. Metalloids are simply in the gray area betwen metals and non-metals.
Here is a picture of some typical metals.
And here is a picture of sulfur, a typical nonmetal.