modis - Image Collection Statistics in Google Earth Engine?

How can I extarct mean of each image collection in google earth engine? for example for this code:

var modis = ee.ImageCollection("MODIS/006/MOD13Q1")
.filterBounds(geometry)

.filterDate("2000-01-01","2001-01-01")
.select("NDVI");

print(modis)

var mod13 = modis.map(function(img){
  return img.multiply(0.0001)
  .copyProperties(img,['system:time_start','system:time_end']);
});