Open a Revit project. Select the level where you would like to import a DWG file. Most DWGs are two-dimensional, whereas the Revit model is three-dimensional, so you must place the DWG by elevation level.
Select the "Insert" tab on the menu ribbon. Select the "Import DWG" icon on the ribbon. A window will open allowing you to browse for your chosen DWG file. Select the file and adjust the import settings at the bottom of the window. You will be able to match the DWG's origin with the Revit origin, as well as modify the import colors of the Revit file. If you prefer to link the file as a cross reference within Revit, be sure to select that option, otherwise the DWG will be imported into Revit as model lines.
Make adjustments to the imported DWG on the given level and draw Revit building components over the imported drawing to convert the drawn image into a three-dimensional BIM model. Use the building components for your DWG to have the parametric functionality of Revit, otherwise you can simply view any three-dimensional DWG elements as component families in Revit.