Suppose your features are Graphic objects.
- Add a mousedown and a mouseup event listeners to the map
- On map mousedown, verify if a feature intersect with a circle centered at the mousedown position (you will have to convert pixel to map units here);
- If there is a drawing feature, add a map mousemove event listener
On map mousemove, modify the geometry of the feature with the position of the cursor (that will be easy for point feature, but more complex for polyline and polygon)
On map mouseup, remove the mousemove event listener