There are several systems of units used, we will talk about the common two
1- SI :- International System of Units
2- US :- United States System of Units

General Units
Equal from the Base Unit
1000,000,000 Giga
1000,000 Mega
1000 Kilo
100 Hecto
10 Deca
0.1
Deci
0.01
Centi
0.001
Milli
0.000 001 Micro
0.000 000 001 Nano

Parameter
Length(L)
Time(t)
Mass(m)
Temperature(T)
SI Units
1m=100cm=1000m m
1hr=60min
1min=60sec
1kg=1000g
US Units
1ft=12in
The Same
1lb=16oz
K=273.15+C F=(K*9/5)-459.67
Convert
1m=3.28ft
1in=2.54cm
1kg=2.2lb
F=(C*9/5)+32
C=(F-32)*5/9

Assistance
Area unit (A)= Square Length units
Volume unit (V) = Cubic Length units
Simple Equation
Velocity (v)= L/t
Acceleration (a)= L/t^2

Density (ρ) = m/V
Force (f) = m*a = P*A (N=0.10197Kgf)
Pressure (P) = F/A = ρ*g*h
(1 bar =100,000 Pa)(1 psi = 6894.8Pa)
Work (W) = F*L (j)
Power (E) = F*V (w)

The fluid properties depend on the type of fluid , fluid temperature and fluid pressure.
The most Important properties for as are the Density (ρ) and the Viscosity (µ)

What is the viscosity? The viscosity is the fluid resistance to flow.
It measured by force the fluid in a known tube and measure the flow rate
(µ) unit is Kg/(m*s) or Pa*s or poise
Poise=0.1 Pa*s

We use this equation for 1-D laminar flow
A1*V1=A2*V2

(P1/ρ*g)+(v1/2*g)+(z1)+(E/mʹ*g)=
(P2/ρ*g)+(v2/2*g)+z2

As we see in the Example there is a pump to take water from Nile to 8 m higher.
Given information:-
Z2 = 8m
Vʹ = 15 l/s
D1 = 154 mm
D2 = 102 mm
ρ = 1000 Kg/mᶾ

Required:-
1- v1 and v2
2- The Pump Power

A1*v1 = A2*v2 = Vʹ = 0.015 m^3/s
A1 = (Π/4)*D1^2 = 0.0186 m^2
A2=(Π/4)*D2^2 = 0.00816 m^2 v1 = Vʹ/A2 = 0.81 m/s v2 = Vʹ/A1 = 1.84 m/s
(P1/ρ*g)+(v1/2*g)+(z1)+(E/mʹ*g) =
(P2/ρ*g)+(v2/2*g)+z2

P1=P2=Pa v1 = 0 z2-z1 = 8m mʹ = ρ*Vʹ = 1000*0.015 = 15 Kg/s
E = mʹ*g*(v2^2/2*g + (z2-z1)) = 1203 w