You can provide us a simple sample with your scenario the next time, so we can help you solve your problem based on that, and please put your post in our sub-forum, so we can easily know which product you are using.
As below is the simple sample code about that:
map.MapUnit = GeographyUnit.DecimalDegree;
InMemoryFeatureLayer layer = new InMemoryFeatureLayer();
layer.ZoomLevelSet.ZoomLevel01.DefaultPointStyle = PointStyles.City1;
layer.ZoomLevelSet.ZoomLevel01.ApplyUntilZoomLevel = ApplyUntilZoomLevel.Level20;
Feature feature1 = new Feature(50, 60);
feature1.ColumnValues.Add("label", "It's a really simple sample to show how to render label on map");
LayerOverlay overlay = new LayerOverlay();
You can find more detail code in our samples.
Wish that's helpful.