How to turn off "autocommit" in PostgreSQL

I am working with PostgreSQL version 11, and would like to turn off autocommit. Either permanently or per query through a PL/PSQL command. In the documentation it says it is turned off by default, elsewhere it says it is turned on by default. Not even the documentation is right about this, as psql does not recognize the config-parameter "autocommit", though the documentation mentions this variable explicitly. Does anyone know how to turn it off? (I am just running tests and "autocommit" might be one of the reasons that hinders performance)