I am amazed to share the First apex class I wrote back in 10/17/2014.
Apex class used to upload an attachment referencing Parent Id in the Visualforce Page.
Salesforce attachment represents a file that a User has uploaded and attached to a parent standard or custom object record. If the user has created permission on a parent object, then only he/she can able to attach an attachment to the parent object.
You can have a look at the amazing video by Jeff Douglas
When Did you code first time and which functionality was that?