Just create a new instance of graphic and add it to the Graphics collection on the featurelayer. If the layer is editable, it will automatically be saved back to the server:
var graphic = new Graphic();
graphic.Geometry = new MapPoint(12,34) { SpatialReference = new SpatialReference(4326) };
graphic.Attributes["Name"] = "Lorem Ipsum";
myFeatureLayer.Graphics.Add(graphic);