? When I get to see the solutions for the problems I like to have another go
? at any I've failed to solve - but to find out whose on move I have to look
? at the answer in the text box on the right.

Wouldn't it be easier to redo these in the tactical archive?

? Also can any one explain what the white triangle to the right of the click
? through tabs does...I notice it changes to a black triangle when I click
? it...but I can't see any effect

Yes, it is connected to the circle! If you click on the circle it will play through the tactic automatically, and by clicking on the triangle you can either get it to play just through the main moves or through both the main moves and the sub variations. It is not very useful except perhaps on the longer Advanced tactics with lots of variations.