How does DNS Leak happen?

Question

Domain Name System

Hello, could you tell me exactly how Dns Leak technically works/occurs?
How can a site get the IP address of my DNS server?

As I understand / remember the work of DNS:
1. I access the dns name that needs to be resolved to my DNS server (it is already further, if necessary, it knocks up ..)
2. if the ip I need is found, then I get it and then I work only with him.

Internet definition,

What is DNS Leak?
This is an IP leak of the DNS server closest to you, which can occur when resolving . DNS queries can bypass your Proxy/VPN/TOR connection, i.e. directly to your ISP's DNS server, which will expose your real location.

DNS leaks can occur through browser or browser add-ons (Flash, Java, WebRTC, Silverlight...).