Questions--standard Visitor Visa

Hi,
My father is living in Pakistan and I want to sponsor him to meet me and my brother and spend a month with us. I am on a spouse visa in the UK. My father will provide his own bank statement but he will be staying with me for a period of one month. I am confused about something.
1) Could please someone guide me about sponsor letter i.e. is there any specific format to make a sponsor letter? and what documents will be submitted along with the sponsor letter?
2) My second question is about bank statement. Could please someone guide me about the exact format of bank statement?