An IP address is a series of numbers which gives a unique identifier to any device connected to the network. It allows the server to locate and retrieve content from the database and to send it back to the client machine (the user).
Because series of alphanumeric values can be hard to remember for humans, we use domain names to map over IP addresses. (i.e: http://www.nytimes.com translates to the following IP address: 184.108.40.206.)
A URL (Uniform Resource Locator) combines a protocol identifier and a domain name to access a specific section of the web (i.e: http://www.nytimes.com)