I'm sorry I don't have videos to cover more of development techniques. I plan to do more but of course I'm a very busy developer so its difficult to find time.
The best advice I can offer you is to study the code for an existing feature, set breakpoints in Visual Studio and step through it and see where the code that does the work is and then examine that code and write similar code for your own needs.
If you're new to C# and ASP.NET and new to mojoPortal its a lot to learn. The more you learn about C# and ASP.NET then it will get much easier for you to understand the code. Also studying the mojoportal code is a good way to learn C# and ASP.NET.
You can create the business logic and data access code for a table using Codesmith Tools and my generation scripts located in the CodesmithTemplates folder inclusded with the source code. There is also an oler freeware version of Codesmith included in codesmith_26.zip. Using this tool you can point my template files at a database table and generate the code to get you started. The table must have a primary key. I think the freeware version will only work with MS SQL but the newer version supports generating agaisnt MySql, or Oracle as well and there may be third party drivers for postgresql.
Hope it helps,