OnItemCreated Event in Sitecore

namespace SitecoreEvents
{
    public class ItemCreatedHandler
    {
        public void OnItemCreated(object sender, EventArgs args)
        {
            var createdArgs = Event.ExtractParameter(args, 0) as ItemCreatedEventArgs;
            Sitecore.Diagnostics.Assert.IsNotNull(createdArgs, "args");
            if (createdArgs != null)
            {
                Sitecore.Diagnostics.Assert.IsNotNull(createdArgs.Item, "item");
                if (createdArgs.Item != null)
                {
                    var addedItem = createdArgs.Item;
                    if (addedItem != null && addedItem.Database.Name.ToLower() == "master")
                    {
                        // Do your action here.
                    }
                }
            }
        }
    }
}
Add below line in web.config file
<event name="item:created">
       <handler type="SitecoreEvents.ItemCreatedHandler, SitecoreEvents" method="OnItemCreated" />
</event>

That's it.
Enjoy Learning.