If it cannot be ordered (for example: yellow, red, green, brown, white), it's nominal scale.
Otherwise, if it can be ordered, but addition is impossible (for example: terrible, bad, neutral, good, excellent), it's ordinal scale.
The ability to order the items allows to compare these with one another (1st, 2nd, 3rd …)
Otherwise, if addition is possible, but multiplication does not make sense, it's interval scale (30° C ≠ 2*15° C, but 30° C + 15° C = 45° C).
Other examples of interval scales are timestamps (but not necessariy time durations), IQ(?), location in Cartesian space, cardinal direction (degrees from North).
Otherwise, if multiplication is possible (has a zero point, for example person's weight), it's ratio scale.
What about discrete values (such as number of children)?
Variables that are measured on the ordinal, interval or ratio scale are quantitative variables while variables that are measured on the nominal scale are qualitiative variables (aka categorical variables).
Measure property
Operators
Possibilities
Central tendency
Nominal
Classification, membership
=, ≠
Grouping
Mode
Ordinal
Comparison, level
<, >
Sorting
Median
Interval
Difference, affinity
+, -
Yardstick
Mean, deviation
Ratio
Magnitude, amount
×, ÷
Ratio
Geometric mean, coefficient of variation
Interval and Ratio scale might be united into Cardinal scale.