These are notes for the fourth video
This video first shows how to make unsigned transactions by unlocking your account. Then a more secure method is shown for creating signed transactions in a secure local environment and then sending them to a test blockchain without ever having your account unlocked and without ever exposing your private key to the Internet.
Make a Local BlockChain
See my instructions for making a local blockchain and for setting up accounts. In the alternative you can use testrpc. If you are using a local block chain then you will need to create 4 accounts in order to experiment with the transactions in this exercise and you will need to mine some play ether into your first account to pay for your transactions. This is all covered at the link above.