Autocomplete ist not available in the Community Edition of Mongo Management Studio.
In aggregation framework queries and the console mode possible commands will be suggested by the application. During input the commands show up automatically after a short amount of time. They can also be displayed manually by pressing CTRL + Space.
Aggregation framework queries
Typical aggregation commands like $group, $add, $sort are shown here.
A list of all MongoDB aggregation framework commands can be found on: http://docs.mongodb.org/manual/meta/aggregation-quick-reference/
Console-mode
There are two possible ways of autocompletion here. First the collections of the actual database is shown after the input of "db." followed by a list of database functions.
After choosing a collection, a list of all collection functions shows up.
A list of all MongoDB database functions can be found on: http://docs.mongodb.org/manual/reference/method/js-database/
A list of all MongoDB collection functions can be found on: http://docs.mongodb.org/manual/reference/method/js-collection/ und http://docs.mongodb.org/manual/reference/method/js-cursor/