I have 2 questions re phone

1. How and what can I use to clean my screen as it gets very dirty with finger marks from me using my finger?

2. Can I connect a USB (with a small end to my phone) and an extension on another and connect that to a USB pen or external USB Hub and say watch videos I have from the stick on my phone?

1) Microfibre Cloth

2) Not out of the box it won't. Have a look around for stuff about USB Host and you'll get an idea.

Been doing it with my
sleve of shirt
Coat (Flece)
Pouch

Would any of this do any damage to my scren ie cause a crack.

Not unless there is something sharp on them it won't hurt - although it's always best with something like a microfibre cloth or similar and nothing abrasive!