why does printing $( gives a number series

Question

When I started with variables to print a variable $foo in a string

I used print ${foo}s but when I used print "$(foo)s" it gave me

1000 4 24 27 30 46 108 125 1000)s . When I printed $( or $) it gives me the sequence 1000 4 24 27 30 46 108 125 1000 . Also $[ gave 5.014002 and $] gave 0 . What do they mean?