基本Rails问题：手动将行插入数据库表

I'm learning Rails and it's going well so far. My biggest question at the moment is: how do I go about manually inserting a row into my database? I've got the scaffolding in place for creating rows of DataTypeOne, but I want a row for DataTypeTwo to be created when the form for DataTypeOne is submitted (and have it reference the id of DataTypeOne...but I think I can work this out on my own).I'm learning Rails and it's going well so far.