The base unit of a tesselation is the Polygon.  When the same polygon is repeated without gaps or overlaps you get a tessellation.

The result is a figure that tessellates

it follows that the sum of the measures of the angles around any vertex must be equal to 360 degrees

if the polygon contains an angle that is not a factor of 360, it will not tessellate

Interior angle of a regular n-sided polygon is [180 × (n-2)] / n