syntax and reasons of generation of DNS query ??

[Aparna]

I am new to  DNS  and am sorry to ask such a silly question but can anyone
please tell me 
1) what are the various ways in which i can generate a DNS query ?

I have  just heard of "nslookup" and "dig" and "host" but 
2) what is or where can i find the exact syntax to use the above ( they look
like commands to me !! ) 

3)what other possible  reasons  could be for  a DNS query  other than the
only one i can imagine " when user types a domain name in the web browser ".
I hope someone finds time to reply bcoz it  will really help me a lot.
Thanx in advance
Aparna.