I am trying to grow mint. I did repot the plant cutting away excess roots. I placed the plant where it gets direct sunshine for about half a day and water the plant occasionally. It does pretty well with leaves showing up in a few weeks.

The questions I have is about "harvesting" the mint leaves. I read about cutting the flowers when the plan starts flowering, but I have no idea what the flowers look like(especially new ones). Also when I cut the leaves off a branch, the branch seems to dry up and die in a few weeks. So I would like to know about which leaves to cut, where (leave a little leave stem, all of the stem, etc.), distribution(all on one stem, location), leaf size, etc.

In the picture below, the plant has plenty of leaves, but the stem on the right seems to be dying because I took all the leaves from that stem?