Merge data from dataframe api reference page into main dataframe page

Author: timsaucer

docs/source/index.rst

@@ -88,3 +88,8 @@ Example
    contributor-guide/introduction
    contributor-guide/ffi
 
+.. _toc.api:
+.. toctree::
+   :hidden:
+   :maxdepth: 1
+   :caption: API

docs/source/user-guide/dataframe/api-reference.rst

@@ -156,8 +156,54 @@ When working in Jupyter notebooks or other environments that support HTML render
 automatically display as formatted HTML tables. For detailed information about customizing HTML 
 rendering, formatting options, and advanced styling, see :doc:`rendering`.
 
+Core Classes
+------------
+
+**DataFrame**
+    The main DataFrame class for building and executing queries.
+
+    See: :py:class:`datafusion.DataFrame`
+
+**SessionContext**
+    The primary entry point for creating DataFrames from various data sources.
+
+    Key methods for DataFrame creation:
+
+    * :py:meth:`~datafusion.SessionContext.read_csv` - Read CSV files
+    * :py:meth:`~datafusion.SessionContext.read_parquet` - Read Parquet files
+    * :py:meth:`~datafusion.SessionContext.read_json` - Read JSON files
+    * :py:meth:`~datafusion.SessionContext.read_avro` - Read Avro files
+    * :py:meth:`~datafusion.SessionContext.table` - Access registered tables
+    * :py:meth:`~datafusion.SessionContext.sql` - Execute SQL queries
+    * :py:meth:`~datafusion.SessionContext.from_pandas` - Create from Pandas DataFrame
+    * :py:meth:`~datafusion.SessionContext.from_arrow` - Create from Arrow data
+
+    See: :py:class:`datafusion.SessionContext`
+
+Expression Classes
+------------------
+
+**Expr**
+    Represents expressions that can be used in DataFrame operations.
+
+    See: :py:class:`datafusion.Expr`
+
+**Functions for creating expressions:**
+
+* :py:func:`datafusion.column` - Reference a column by name
+* :py:func:`datafusion.literal` - Create a literal value expression
+
+Built-in Functions
+------------------
+
+DataFusion provides many built-in functions for data manipulation:
+
+* :py:mod:`datafusion.functions` - Mathematical, string, date/time, and aggregation functions
+
+For a complete list of available functions, see the :py:mod:`datafusion.functions` module documentation.
+
+
 .. toctree::
    :maxdepth: 1
 
    rendering
-   api-reference