Ignoring some kind of auto completition and showing visited URLs that match while typing this will happen when clicking return:
The browser will parse the URL and split it into different parts (see
Uniform Resource Locator - Wikipedia, the free encyclopedia[
^] for the parts). Missing optional parts will be initiliased with defaults (scheme/protocol: HTTP, port: default port for protocol, e.g. 80 with HTTP).
The browser than queries the IP address for the host part using DNS if the host part is not already an IP address. If that is successful he will connect the server using the IP address and port number.
The following communication depends on the used protocol.