messageChoice- When you want to display a list of values in a drop down fashion then you use the messageChoice. see also:http://newtonapples.com/message-choice/
messageLovInput- when you want the uses to select from a list of values and quick select from the values then we use the messageLovInput.This will open a pop up and you can search for values and select from the results.
messageDownload- Used when the user needs to download a file or attachment.
messageFileUpload- Used for displaying a button with a messageTextInput .User can browse from the local machine and upload a file using this.
button- It is a general button which has an action associated with it.You can set the fire action property which will inturn call a method which will perform that action.
submitButton- This is the button used when you want to submit data to a OAF page.
Link- Used for creating links.There are many types of links that can be created.
formValue- This is used to send value to an OAF page but without being displayed in the page.
spacer- This is used when you want to add space between your items placed in the page.
seperator- This creates a horizontal line in an oaf page.
Flex- This is a flexfield.There are 2 types of flexfields. Key and Descriptive flex fields.