// 1. load landsat 8 data

var image = ee.ImageCollection('LANDSAT/LC08/C01/T1_SR')

???.filterDate('2018-01-01','2018-12-31')

???.filterBounds(roi)

???.sort('CLOUD_COVER')

???.first();

??

// 2. visialization parameter

var vis = {bands:['B4','B3','B2'],min:0,max:3000,gama:1.4};

Map.addLayer(image,vis,"my landsat 8 in 2018");

Map.addLayer(image.clip(roi),vis,'landsat image in my roi');

Map.centerObject(roi,8);

//var myimage = image.clip(roi);

//Map.addLayer(myimage,vis,"myimage");

// 3. to my drive not yours

Export.image.toDrive({

?image:image.int16(),

?description:"landsat2018",

?scale:30,

?region:roi,

?maxPixels:1e13

});