On our front porch of our house, the supports holding the roof up are beginning to rot out at the bottom. I would like to replace them son, but have no idea where to start. I have the materials at least.

Do I begin by jacking up/supporting the roof over the porch I am guessing?
D the supports generally attach to the roof in some way, or are they held there by the weight, or "force" of the roof?

Any pointers/tips before I get started would be greatly appreciated. Thanks!