We will take a look a git bisect from a practical perspective. This will be a very simple demo, but should at least show you how this tool can help you to track down erroneous code in your git history. Let's create a new folder (name it bisect_demo) and create a series of commits.
git init
echo "Space, the final frontier" > monologue.txt
git add ./monologue.txt && git commit -am "first line"
echo "These are the voyages of the Starship Enterprise" >> monologue.txt && git commit -am "second line"
echo "Its five years mission" >> monologue.txt && git commit -am "third line"
echo "To explore strange new worlds" >> monologue.txt && git commit -am "fourth line"
echo "To seek out new life" >> monologue.txt && git commit -am "fifth line"