Here ia configuration example. You need to cahnge your IP addresses and your interface numbers.
ip dhcp excluded-address 10.1.1.1
!
ip dhcp pool DHCPPOOL
network 10.1.1.0 255.255.255.0
default-router 10.1.1.1
dns-server #.#.#.#
!
interface FastEthernet0/0
ip address 10.1.1.1 255.255.255.0
ip nat inside
!
interface Serial0/0
ip address #.#.#.# #.#.#.#
ip nat outside
!
ip local pool DHCPPOOL 10.1.1.2 10.1.1.254
ip nat inside source list 100 interface serial0/0 overload
!
access-list 100 permit ip 10.1.1.0 0.0.0.255 any