DOCS-#3795: Expand using_pandas_on_dask.rst doc (#3808)

Signed-off-by: Alexey Prutskov <alexey.prutskov@intel.com>

docs/developer/using_pandas_on_dask.rst

@@ -1,8 +1,23 @@
 pandas on Dask
 ==============
 
-The Dask engine and documentation could use your help! Consider opening a
-`pull request`_ or an issue_ to contribute or ask clarifying questions.
+This section describes usage related documents for the pandas on Dask component of Modin.
 
-.. _pull request: https://github.com/modin-project/modin/pulls
-.. _issue: https://github.com/modin-project/modin/issues
+Modin uses pandas as a primary memory format of the underlying partitions and optimizes queries
+ingested from the API layer in a specific way to this format. Thus, there is no need to care of choosing it
+but you can explicitly specify it anyway as shown below.
+
+One of the execution engines that Modin uses is Dask. To enable the pandas on Dask execution you should set the following environment variables:
+
+.. code-block:: bash
+
+   export MODIN_ENGINE=dask
+   export MODIN_STORAGE_FORMAT=pandas
+
+or turn them on in source code:
+
+.. code-block:: python
+
+   import modin.config as cfg
+   cfg.Engine.put('dask')
+   cfg.StorageFormat.put('pandas')