Implicit Conversion perform automatically in VB.NET, that is the compiler is taking care of the conversion.
The following example you can see how it happen.
1. Dim iDbl As Double
2. Dim iInt As Integer
3. iDbl = 9.123
4. MsgBox("The value of iDbl is " iDbl)
5. iInt = iDbl
6. MsgBox("The value of iInt is " iInt)
Explicit Type Conversions
In some cases we have to perform conversions , that is the compiler does not automatically convert a type to another . These type of conversion is called Explicit conversion . An explicit conversion uses a type conversion keyword. With these conversion keywords we have to perform the Explicit Conversion.
String.Format(), creates strings by combining string values with other data types and controlling how each value is displayed. Rather than formatting values individually and then concatenating them, Format() works with a string that specifies insertion points in its text. These insertion points are then replaced with the actual values. Being a string itself, the format string can be loaded from external files and resources, allowing for flexible string handling that can be convenient when working with internationalized and localized applications.
Format specifiers are special symbols that specify the way data is formatted during its conversion to a string. This topic describes frequently used standard and custom format specifiers used to format numeric and date/time values.
Table A-1 Variables Prefixes Prefix | Data Type | byt | Byte | b | Boolean | cur | Currency | d | Double | dte | Date | f | Single | hf | File handle (Long) | hwnd | Window handle (Long) | h(... lowercase) | Handle to something (Long) | l | Long | n | Integer | o | Object | s | String | v | Variant |
Table A-2 Modifiers and Special Types Prefixes Prefix | Data Type | a | Array <of another type> | C | Class or class instance | t | User-defined type or instance | e | Enumerated type or instance | p | Pointer (used with API calls) | pcb | Pointer to a callback function (used with AddressOf) |
Variables are declared using the Visual Basic Dim keyword. The syntax for a simple declaration of a variable is as follows:
Dim variableName As variableType

Option Explicit statement ensures whether the compiler requires all variables to be explicitly declared or not before it use in the program.
The Option Explicit has two modes. On and Off mode. If Option Explicit mode in ON , you have to declare all the variable before you use it in the program . If not , it will generate a compile-time error whenever a variable that has not been declared is encountered .If the Option Explicit mode is OFF , Vb.Net automatically create a variable whenever it sees a variable without proper declaration.
By default the Option Explicit is On
With the Option Explicit On , you can reduce the possible errors that result from misspelled variable names. Because in Option Explicit On mode you have to declare each variable in the program for storing data.
Option Infer
Enables the use of local type inference in declaring variables.
On - Optional. Enables local type inference.
Off - Optional. Disables local type inference.
Constraints
Which restrict values that are allowed to be stored in table fields. In general, constraints are used to restrict values in tables, make validation checks on one or more fields in a table, or even check values between fields in different tables.
TryParse.
This class contains methods that allow you to convert string representations of numbers into numeric data type that computers can manipulate.
Scope
A local variable only exists while the function it is local to (the one you declared it in) is executing. It vanishes when the function returns, and reappears (with some different value) when the function executes later. If you call the function recursively, each call of the function has its own value for the local variable. You may also declare a variable to be local to a block, in which case it exists only while code inside the block is executing. A local variable so declared only has meaning inside the function or block it is local to.
A global variable exists independently of any function. Any function may use it. If functions declared in different source files use the same global variable, the variable must be declared in both source files (or in files #included by both files) before its first use. If the two files have different initializations for the variable, only the first initialization has effect.