Tutorials covering iteration, lists and debugging?



I'm new to Maxima and learning it on my own.

This a only slightly contrived example of what causes me grief.
(%i1) numer: true$
dTHETA: (2 * %PI/10)$
THETA: 0$
table: makelist()$
for j: 0 step (dTHETA) thru ( 2 * %PI) do
   ( table: append(table,[sin(THETA)]),
      THETA: THETA + dTHETA);
table;
THETA;
dTHETA;


(%i2)
(%i3)
(%i4)
(%i5)
Unable to evaluate predicate 0 > 2*%PI
  -- an error. To debug this try: debugmode(true);
(%i6)
(%o6) []
(%i7)
(%o7) 0
(%i8)
(%o8) 0.2*%PI

Why the error at %i5 ?
Why isn't %o8 showing a floating point representation?

TIA