How to use concate, lappend and append in tcl-tk?

p15.tcl

#!usr/local/bin/tclsh
set var {1 2 3}
puts "output of concat: [concat $var {3 6}]"

puts "output of lappend: [lappend $var {3 6}]"

puts "output of append: [append $var {3 6}]"

output:

:chmod 755 p15.tcl

:tclsh p15.tcl

output of concat: 1 2 3 3 6

output of lappend: {3 6}

output of append: {3 6}3 6