Install the japro_entities.def inside your gamedata/japro/scripts folder (make sure that gamedata folder is the same as GTKs basepath when you do file->project settings).
In file->project settings, select Custom JA modification as the mod, japro as the fs_game, and multiplayer mapping mode.
Restart GTK, and you should be able to see/create the japro entities by right clicking the grid and looking at the df_ entities.
New brush entities: df_trigger_start, df_trigger_checkpoint, df_trigger_finish, trigger_newpush.
New non-brush entities: target_restrict.