if in Kotlin looks exactly like any other C-style language:

if (2 > 1) { //Boolean expression
    println("2 is greater than 1")
} else {
    println("This never gonna happen")
}

In Kotlin, if (and when) is an expression. It means that the if statement returns a value:

val message = if (2 > 1) {
    "2 is greater than 1"
} else {
    "This never gonna happen"
}

println(message)

Kotlin doesn't have ternary expressions, but an if expression can be written in a single line:

println(if(2 > 1) "2 is greater than 1" else "This never gonna happen")