I'm not understanding about the topic fundamental and derived units.
The fundamental units are units used in measurement that are arbitrarily determined and internationally accepted. There are seven in number as follows:
Length (meter) m
Mass (kilogram) Kg
Time (second) s
Electric Current (ampere) A
Thermodynamic Temperature (degrees Kelvin) K
Amount of substance (mole) mol
Luminous Intensity (candela) cd
Derived units are defined in terms of the fundamental units via a system of quantity equations. Here a few examples:
Area (square meters)
Volume (cubic meters)
Velocity (meter per second)
Acceleration (meters per second per second)
Mass Density (kilograms per cubic meter)
Luminance (candelas per square meter)
Current Density (amperes per square meter)
Derived quantities are products and/or ratios of the fundamental quantities that exist in a system of units. ... The corresponding units are meter, kilogram, second, Ampere, Kelvin, mole, and candela. One derived quantity is the meter per second, which are unitsof velocity and is a simple ratio: