An IP address is the unique identifier assigned to every device on a network. Every device needs to have their own address in order to be able to communicate with each other. IP addresses are in dotted decimal notation and look like this: 192.168.1.1
The subnet mask portion is there to determine which subnet you belong to. It basically determine the range of addresses on your portion of that network. Subnet masks are also in dotted decimal notation and look like this as well: 255.255.255.0
The default gateway is used as exactly that, a gateway which knows how to get you to IP addresses not on your network.
I am sure you know the difference between the words “preferred” and “alternative” so I will just explain the DNS bit.
DNS is Domain Name System. It is used to either translate friendly names like computer names or website addresses (URLs) into IP address, or the reverse, IP addresses into names.