Star Citizen is a mixture of MMO and RPG. You can play with or against other players there. Any MMO game allows players to communicate not only using chat but also use special emotes. This is a standard practice and Star Citizen also has list of great emotes you can use while playing. Here you can filnd the list of all available emotes.
First of all press F12 to open chat. Then type which emotion you would like to show. As you can see below some of them have digits. That means that several modifications of this emotion are available. You can specify which one you wish to use by typing a number after the emotion. For example /clap 2 differs from /clap 3. If you type it without number a random modification will be used.
Here is a list of all the emotes in Star Citizen: