OK, so these are probably going to be stupid questions, but I have looked everywhere in the manual and cannot find.

I have just got the phone and de-branded it. On the home screen there is a lock symbol in the bottom right, which you can touch and will go from locked to unlock, but I cannot figure out what it is for, as it seems to make no difference.

Also, the 3 screens that you should be able to have available, I do not have the 3 boxes unless I select the arrow for the widgets, and then they appear.

If these are really stupid, then please give me a virtual slap .. :-)

Hiya - this is to allow you to move the widgets about (unlocked) or lock them in place.
I agree, only when you open up the widgets bar, then the 3 screens appear. Seems daft to me too... I don't use the widgets screen at all, in fact, I just like the 4 icons across the top (it's one of the homescren options) and the 4 fixed icons at the bottom.
My opinion/choice is that I like to see my homescreen picture rather than having widgets obscuring it!
I'd like to customise the 4 icons at the top (on that version of the homescreen theme) but can only put programs there. I haven't figured out how to e.g. have a WiFi wizard shortcut or whatever, as yet. I used the Widgets based homescreen for about a day, but it just felt clunky - also, a lot of widgets don't antialias e.g. the Profiles widget is awful & takes up most of the screen when opened and the text is quite pxellated, not smooth. Ruins the aesthetic a bit!
just my penny's worth...