Usage of the Particle で alone and with は


I understand what the particle で does as far as describing how or where an
action took place. But I notice that I run into で many other times where it
seems to have a different function.

Could someone help clarify the uses of で? Specifically its uses other than
describing how/where an action occurred.

An example would be something like this:

> 必ず届くこのいっしゅんのひかりで

Or as used in では, or じゃ. I know what it means in conjugations for adjectives
and such, but I often see just では following other words like nouns with no
verb after it or any thing. In the case where it's alone like that, what does
it mean?

