set ns [new Simulator] ;# Simulator instance
$ns at 5.0 “add1”
set a 10
set b 15
proc add1 {} {
global a b ns
set currentTime [$ns now]
puts "Current Time=$currentTime"
set value [expr $a+$b]
puts "value = $value"
}

set ns [new Simulator] ;# Simulator instance
$ns at 5.0 "add2 10 40" ;# Calling add2 at 5.0
$ns at 12.0 "add2 10 50" ;# Calling add2 at 12.0
proc add2 {p q} {
global ns
set result [expr $p*$q]
puts "result=$result"
}
where,
ns → Simulator instance
global → Accessing the outside variable
now → Return the current execution time of the procedure