Added some Comments

Author: AmanKumarVerma11

first.kt

@@ -1,3 +1,28 @@
+/*  
+!Create a birthday message in Kotlin
+
+?Introduction
+    >In this program you will create a short Kotlin program that prints a birthday message with a cake and a birthday banner.
+
+?Prerequisites
+    >How to open and edit code in https://developer.android.com/training/kotlinplayground, a browser-based Kotlin programming tool.
+    >Understand the "Hello world!" program from the Write your first Kotlin program codelab.
+    >How to use println() to write text to the console of the online Kotlin code editor.
+
+?What you will learn
+    > How to print more complex text from your program.
+    > How to do basic math in Kotlin and store the results in variables for later use.
+    > How to create a function to print the same string several times.
+    > How to create a loop that prints a text snippet multiple times.
+
+?What you will build
+    > You will create a short program that you can use to print birthday messages, a text-based picture of a cake, and a banner.
+
+?What you need
+    > A computer with internet access and a modern web browser, such as the latest version of Chrome.
+
+*Written by Google Developers Training team.
+ */
 fun main() {
     println("Hello, \nworld!")
     println("Janshi")

fourth.kt

@@ -1,7 +1,11 @@
 // !Modify a function to have two arguments
+/* 
+ Important: A variable declared using the val keyword can only be set once. You cannot change its value later in the program.
+ You can declare a changeable variable with the var keyword
+ */
 fun main() {
     val border = "`-._,-'"
-    val timesToRepeat = 4
+    var timesToRepeat = 4
     printBorder(border, timesToRepeat)
     println("  Happy Birthday, Jhansi!")
     printBorder(border, timesToRepeat)

sec.kt

@@ -1,4 +1,4 @@
-//In this we used function inside a function, we can return a function or rather use it normally.
+// !In this we used function inside a function, we can return a function or rather use it normally.
 fun main() {
     println("Hello, world!\n")
     birthdayMessage()