Can you explain How does the "MODE" key work?

The [MODE] key can be used to select the modes described below.
Important! The following is a general explanation of Scientific Calculator modes. Note that your calculator may not include all of the modes described here.
1) Calculation Modes
Before performing a calculation, you first need to select the appropriate calculation mode.
COMP: Basic arithmetric calculations
(arithmetic operations, trigonometric functions, etc.)
COMPLEX: Complex number calculations
SD: Single-variable statistical calculations
(sample standard deviation, etc.)
LR or REG: Paired-variable statistical calculations
(linear regression statistical calculations, etc.)
BASE or BASE-n: Binary, octal, decimal, hexadecimal number system calculations
MAT: Matrix calculations (determinants, etc.)
VCT: Vector calculations
EQU: nth degree equations, simultaneous equations
2) Display Settings
Use these settings to control how calculation results are displayed.
Note that changing the Fix and Sci settings does not affect internal calculation results.
Norm: Exponential display format and cancels the currently configured Fix and Sci settings.
Fix: Specifies a fixed number of digits to the right of the decimal place.
Sci: Specifies a fixed number of significant digits.
3) Angle Unit Setting
(90°=?/2 radians=100 grads)
Deg: Degrees
Rad: Radians
Gra: Grads
4) Engineering Mode
Use this mode when you want to input and perform calculations using engineering symbols.