Aliases are handy shortcuts you can use when communicating with text pilots. They consist of a dot command, which is a period followed by any number of characters without whitespace (as in ".ccvxm"), followed by up to 9 optional parameters (such as ".ccvxm 5,000 1a"). Entering the latter command will send the pilot the radio message "climb via SID except maintain 5,000. Departure frequency 124.500, squawk [assigned squawk].". You can see how this could save some time and hassle.
Aliases are defined in the alias file, which you should have downloaded from the controller downloads page and imported in VRC. The file consists of text only and is easy to read once you are familiar with the alias variables and functions published here. In the pages of this section, you can find lists of aliases relevant to general controlling and specific positions. These lists may not be exhaustive, so consult the alias file itself if you want to learn more.
.info [code] [airport] - Provide the pilot with the given ATIS code at the airport you specify.
Above is an example alias description, in this case involving the current ATIS code at a given airport. The alias syntax is in bold. Words in square brackets are where you type in the relevant information. You must type the information in the correct order for the alias to work properly. If the ATIS code at KLAX is W, you would type ".info w klax" into the command line. To the right of the syntax is a short description of what the alias does, which in this case will let the pilot know that W is current. Multiple similar aliases may be combined into one description, in which case they will be separated by the pipe character, "|", as in ".type | .equip | .typeequip".
For aliases that are directed at a specific pilot, they must first be radio selected, just as when typing a message by hand. In VRC, you can click on the aircraft or you can type the callsign and push the aircraft select key (numpad plus by default). The selected aircraft's callsign will be displayed in the lower left corner of the main window. When you send a radio message, the aircraft's callsign will be added to the beginning of the message and the pilot will hear a sound letting them know you are addressing them directly. Some aliases, such as ".closed", are intended to notify all pilots on frequency, in which case you should first use the escape key to deselect any aircraft you have selected. This will be noted in the alias description.