This article will give you a clear understanding of what propagation is. Any time DNS changes are made, you must wait for propagation to complete before you seeing any changes. Propagation is the time it takes DNS servers and Internet Service Providers to update DNS tables to reflect any new website changes. During propagation, one ISP may be able to access a site, but not another ISP. Also, yourdomain.name might work while www.yourdomain.name does not work. All of this is normal during propagation.
DNS stands for Domain Name Service. Whenever you visit a website using a domain name, you use DNS. Your ISP administers your request for a domain name to your primary or secondary DNS server. Your DNS server checks if it knows the IP address the domain is pointing to. If the server does not know the IP address, it sends a query to the Root DNS servers. The Root server tells the DNS server which DNS servers are Authoritative for the domain. The Authoritative DNS server tells the local DNS server which IP address the domain is at. The local DNS server then makes a copy of this information. This process speeds up future queries and reduces the load on Root servers. It is the caching process that leads to propagation. However, DNS servers do not keep the information forever. It keeps the information for a certain amount of time and then deletes it. The next time you visit that domain (after the information has been deleted), the process starts all over. This process is called propagation and may take anywhere from 12-72 hours.