The most basic way to communicate is through the SAY command. This will transmit your message to whoever is in the same location as yourself. Thus, SAY Hello would produce the action of you saying "Hello" to all present. No quotation marks are necessary, but make sure there is someone to talk to before using SAY (use the LOOK or GLANCE command to see if anybody is present), or you could find you are talking to yourself! The SAY command may also be abbreviated to simply a single apostrophe or quotation mark, followed by the text of your message. Using SAY is plainly the most sociable form of communication when more than one person is in the same location as you since all present can be involved in the conversation. If you wish to say something to a specific person in particular, use SAY TO followed by the name of the person, providing they are in the same location as you.
See: HELP SPEAKING for the main help-file on forms of communication, with HELP COMMUNICATION the non-beginner summary; HELP CALLING with details of calling channels and HELP TELLS, HELP SHOUTING and HELP ADVICE for specifics on various ways to make yourself heard.