Domains work through a network of name servers. Each domain typically has a pair of name servers that "know" about them. The name servers need time "talking" to each other to find out about each of their domains.
This process can take anywhere between 24 and 72 hours.
Most of the time, domains will start working after 24 hours of the name servers you made through your domain name registrar.
However, it can take as long as 72 hours as well.
If, after 24 hours, your domain doesn't work, please continue to wait another 48 hours for your domain to work.
A key part of your domain name's configuration is making sure that your name servers are set correctly.
If your domain doesn't function after 72 hours, you should double-check with your registrar that your name servers were entered correctly (as well as the IP addresses of the name servers if they were given to you).