So, when you make eatable stew you use fresh water, right?

Yes, use fresh water for anything edible, and salt water for anything else.

Making cloth. How is that done?
I have a concoction in the pot with nine pieces of the vine.

Send a villager to the pot and pay attention to what they "say". It will guide you as to what to do next.

You need to clear the rocks from the pit near the fruit trees. Then have villager bring hot rocks. Cover them with large leaves from near the science lab. Then you bring a villager to one of the trees and they will shake some fruit down and put it into the pit.

It says unfinished stew is cooking.

This is the Puzzle 7

Here, it seems that you are beginning to solve the Puzzle 11

The link doesn't work

Unfortunately, that is one of the many, many links broken in the Great Forum Crash of 2011. Unfortunately, there were far too many broken links to fix them all.

The topic I linked to describes how to reach any of the posts affected by that crash, and the one you want can be found at this link: http://www.ldwforums.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=217089