Also, for ease of use when working with sections etc., activate the "Show open/close icon for cell groups" checkbox under Edit->Preferences. This adds a toggle chevron on the left side.
The frontend encourages/enforces you to break long code passages into smaller parts, which is not always a bad idea, especially for testing and debugging (although debugging in Mathematica is something of a sore point when you are used to other systems). Still, a solution for in-cell partitioning would be nice-to-have.
There is also some option to format sections so that a click on their content toggles open/close instead of just the tiny triangle, but I can´t remember at the moment how that worked. Perhaps someone will chip in here.