SharePoint is a massive product. It is so huge which makes it difficult to know all parts of it. Having said that you need to know the product and be a good user of the product itself then you can try a path to make yourself professional in this product. I believe there are two types of professionalism in SharePoint. The first one is Administration and Configuration of SharePoint. The second one is Development and Customization of SharePoint. These are steps to be a professional programmer in SharePoint:
1- Know the product and the functionality of it and the purpose
2- Be a good user of it (know how to use SharePoint)
3- Know how to install a SharePoint Server
4- Be able to understand differences between MOSS and WSS
5- Know how to use Out of the box features
6- Match the features to your company or a company
7- Understand different types of sites in SharePoint
8- Understand the connection of SharePoint and Office box
9- Be professional on creating Simple InfoPath forms
10- Configure a server farm
11- Create and manage content
12- Create a workflow
13- Manage enterprise search and indexing
14- Do Backup and recovery
15- Create a BDC
16- Develop a security topology
17- Configure other server platform to work with SharePoint
18- Know how to migrate from 2003 to 2007
19- Build collaboration and publish portals
20- Customize and brand your site with MasterPage, PageLayout, CSS, Themes and navigation
21- Customize and Create Workflow
22- How to deploy a workflow across servers
23- How to Use Form servers
24- How to use Excel Services
25- How to create Solution Package
26- How to use VS to Create Solutions
I am sure there are so many items that I missed and I need your help to add more if you think I missed something just send a post and I will add it to the list.
Anyway it is a long way to know SharePoint. At the first step my suggestion is that you can see 32 movies from Microsoft site to help you understand very basic functionalities of SharePoint.Just remember these movies are not covering all the functionalities but just part of them.
This is the site you can see these movies: http://office.microsoft.com/en-us/sharepointserver/CH102066971033.aspx?stt=1
This is the list of movies to help you to get an understanding of basic features.
Demo: Configure a SharePoint Server 2007 site to receive e-mail
Demo: Deploy an administrator-approved form template
Demo: Simplify collaboration with a SharePoint team site
Demo: Streamline business processes with forms and workflows
Watch this: Create a presentation from slides in a slide library
Watch this: Create and manage a SharePoint calendar
Watch this: Find your way around a SharePoint team site
Watch this: Customize a site
Watch this: Automate business process with workflows
Watch This: Tour of My Site
Watch this: Use Word 2007 to post to a SharePoint blog
Watch this: Create a recurring meeting with a Meeting Workspace in a SharePoint calendar and then connect it to Outlook 2007
Watch this: Different ways to check documents in and out of a SharePoint site
Watch this: Make it easier to find information with views
Demo: The new SharePoint Server 2007 Fluent interface
Demo: Prepare to back up files on Office SharePoint Server
Demo: Connect people to information with portals
Demo: Enterprise Content Management with SharePoint Server 2007
Demo: Search for information on a SharePoint site
Demo: Add KPIs to your SharePoint site
Demo: Back Up Office SharePoint 2007
Watch this: Using SharePoint to manage your classroom
Demo: Display KPIs in a dashboard
Watch this: Give a user access to a SharePoint site
Watch this: Work with documents offline in Outlook
Watch this: Find just the data you need by using Filter Web Parts in a dashboard
Watch this: Use a Document Workspace to collaborate on a document from a SharePoint library
Demo: Enable Excel Services and data connections for a SharePoint team site
Demo: Make better business decisions with reports and dashboards
Watch this: Manage access to documents on My Site
Watch this: Use an approval workflow in SharePoint Server 2007
Watch this: Create and publish Web pages on a publishing site