Export Error-GEE

Question

When I try to export I am facing the error stating:

"Unknown element type provided: string. Expected: ee.Image, ee.ImageCollection, ee.FeatureCollection, ee.Element or ee.ComputedObject."

var s2 = ee.ImageCollection("COPERNICUS/S2");
var filtered = s2.filter(ee.Filter.lt('CLOUDY_PIXEL_PERCENTAGE', 30))
  .filter(ee.Filter.date('2016-01-01', '2016-12-31'))
  .filter(ee.Filter.bounds(studyArea))
var image = filtered.median().clip(studyArea); 
Map.centerObject(studyArea, 10)
var ndvi = image.normalizedDifference(['B8', 'B4']).rename(['ndvi']);
Map.addLayer(ndvi);
var mndwi = image.normalizedDifference(['B3', 'B11']).rename(['mndwi']);
Map.addLayer(mndwi);
var awei = image.expression(
    '4*(GREEN - SWIR1) - (0.25*NIR + 2.75*SWIR2)', {
      'GREEN': image.select('B3').multiply(0.0001),
      'NIR': image.select('B8').multiply(0.0001),
      'SWIR1': image.select('B11').multiply(0.0001),
      'SWIR2': image.select('B12').multiply(0.0001),
}).rename('awei');
//Map.addLayer(awei);
// Simple Thresholding
var waterMndwi = mndwi.gt(0)
var waterAwei = awei.gt(0)
Map.addLayer(waterMndwi);
Map.addLayer(waterAwei);
// Combining Multiple Conditions
var waterMultiple = ndvi.lt(0).and(mndwi.gt(0))

// Export the image to Drive
Export.image.toDrive({
  image: 'waterMndwi',
  description: 'Mndwi',
  scale: 30,
  region: studyArea
});

Answer 1

The error is pretty self explanatory: you are trying to export a object that is of type string: 'waterMndwi'. But your export function only takes featureCollections, imageCollections etc. So you have to provide the object without the quotations:

Export.image.toDrive({
  image: waterMndwi,
  description: 'Mndwi',
  scale: 30,
  region: studyArea
});

You probably want to go through some tutorials: https://developers.google.com/earth-engine/tutorials/tutorials