I am looking for a document, web page etc that explains, in words and
pictures, the task types used in today's SSA sanctioned competitions?
Yes there is an explanation in the rule book, below is from the 2010
sports class rule book, but it is not easy to understand or visualize
for us newbies.

Thanks in advance

From the 2010 Sports Class rulebook

10.3.2 Task Types
10.3.2.1 Assigned Task - not used.
10.3.2.2 Modified Assigned Task (MAT) - Speed over a course of one
or more turnpoints, with a finish at the contest site.
10.3.2.2.1 The CD shall designate a minimum flight time.
10.3.2.2.2 The CD may designate from zero to 11 turnpoints. Designated
turnpoints must be attempted in the designated
sequence, but a pilot may elect to finish after any turnpoint in the
sequence.
10.3.2.2.3 A pilot who achieves all designated turnpoints may elect to
fly to additional turnpoints. Such pilot-selected turnpoints
must comply with any restrictions the CD has imposed under Rule
10.3.2.2.4, and no turnpoint may be repeated unless at least
two intervening turnpoints are claimed (the Start and the Finish are
not turnpoints).
10.3.2.2.4 The CD may restrict:
• The maximum number of turnpoints to a number less than the normal
maximum of 11
• The number of times any particular turnpoint may be claimed
• The choice of the first turnpoint (applies only if the CD designates
no turnpoints per Rule 10.3.2.2.2)
10.3.2.2.5 ‡ The CD may designate a final turnpoint that all pilots
must use immediately prior to a finish. This final turnpoint
shall be no further than 10 miles from the finish (gate or cylinder
center).
10.3.2.3 Turn Area Task (TAT) - Speed over a course through one or
more turn areas, with a finish at the contest site.
10.3.2.3.1 Turn areas are turnpoints with a designated radius defining
a cylinder.
10.3.2.3.2 The CD shall designate a minimum flight time, a sequence of
one or more turnpoints and a radius for each which
shall be an integral number of miles not greater than 30.
10.3.2.3.3 Turnpoint cylinders shall be chosen so that no task leg can
be shorter than the restrictions imposed by Rule 10.3.1.1