Please find the code with some explanations here:

fun main() {

    println("Hello, world!!!")

    // This is a comment. Comments start with //

    // val is used for variables which are immutable (not changable)

    val myName = "Denis"

    // myName = "Michael" // ERROR: Val cannot be reassigned



    /* This is a multi line comment starts with /* and ends with *'/ without the '

     var is used for variables which are mutable/changeable.

     kotlin is a strongly typed language that supports Type Inference.

     The compiler will directly assume the size and type to a variable by that.

     For example, if you assign any whole number to a variable,

     the compiler will directly assume that the variable is of type Int

    */ */

    var myAge = 31



    // Integer TYPES: Byte (8 bit), Short (16 bit), Int (32 bit), Long (64 bit)

    val myByte: Byte = 13

    val myShort: Short = 125

    val myInt: Int = 123123123

    val myLong: Long = 12_039_812_309_487_120



    // Floating Point number Types: Float (32 bit), Double (64 bit)

    val myFloat: Float = 13.37F

    val myDouble: Double = 3.14159265358979323846



    // Booleans the type Boolean is used to represent logical values.

    // It can have two possible values true and false.

    var isSunny: Boolean = true

    // not sunny anymore...

    isSunny = false



    // Characters

    val letterChar = 'A'

    val digitChar = '1'



    // Strings

    val myStr = "Hello World"

    var firCharInStr = myStr[0]

    var lastCharInStr = myStr[myStr.length - 1]

}