Simple feature editing is supported by the ArcGIS API for JavaScript when working against data stored in an enterprise geodatabase format. What this means is that your data needs to be stored in an enterprise geodatabase managed by ArcSDE.
Editing works on the concept of last in wins. For example, if two people are editing the same feature in a layer, and both submit modifications the last editor to submit changes will overwrite any changes made by the first editor. Obviously this could pose a problem in some cases so before implementing editing in your application you will need to examine how your data could be affected.
Other characteristics of editing include support for domains and subtypes, template style editing, and the ability to edit stand-alone tables and attachments. To use editing you will need to use a FeatureService and a FeatureLayer. Editing requests are submitted to the server using an HTTP Post request which in most cases will require the use of a proxy.