Use all four operations to solve problems involving measure [for example, length, mass, volume, money] using decimal notation, including scaling

What this means, in plain words

A decimal writes parts of a whole using the places after the point: tenths, then hundredths, then thousandths.

Capacity is how much a container holds. Volume is how much space something takes up.

Mass is how much there is of something, measured here in grams and kilograms.