I think you are using LiveView Web. If so, to build a query, you can either
1) simply type it into the query text box area
2) use the query builder (use each part of the gui to pick a table and then add conditions)
The query syntax is LiveQL (fully described in the doc set here)
Note: the query builder gui does not currently have an interface for guiding you through using "group by". If you know you want a group by query, you need to type that query into the query box yourself.
I think it will be important for future users of Community Answers to know that we're talking about LiveView Web as of release 1.0.2, just in case the LiveView Web Query Builder does support Group By in some further release.