vat and expenses enquiry

hi, im starting my own business and dont know much about expenses that i can claim back or worst what the difference is between expenses and VAT. So for example, if i fueled my car for £10.00 and was charged VAT aswell, so when claiming expenses, do i get my £10.00 back or just the VAT on the petrol???

This is very important and what about car space of office rent??? how would i claim that back??? would i claim back the rent as a business expence or the VAT on the rent???

Please help me.

Soni