IP is a number with 4 sections that each section is a number among 0-255 like :124.103.81.16. Each computer has a particular IP that show its address in internet.You can find your IP in this address :run-->command line-->IP config.

DNS is the abbreviation of "Domain Name Server" that server keep list of IP in DNS.If indicated IP wasn't in server's DNS server ask about IP from another server and ultimately find IP

FTP is a protocole for sending files to web. You can use FTP with this structure: ftp://[ ] which you must type address of your destination in[ ] like: ftp://ce.sharif.edu/~jalal.