A bank will lend you money to buy a house. They will set an interest rate for you to pay back the money they lent you. This interest rate is called the "fixed" rate. But, after a certain amount of time, this fixed rate changes to a new, "variable" rate. The variable rate can change every month or every year. This is called an "adjustable" rate mortgage.
A credit union is a bank that is owned by its members. It gives out loans to its members at a lower interest rate than other banks, and it also has a savings account where you can save money for the future. The only difference between a credit union and a regular bank is that the people who use the credit union are also the owners of it, and the money they save in their accounts goes back into the credit union to help other members.
The steepest direction to go down is the direction where the hill is the steepest. In gradient descent, we start at a random point and move down in the direction of steepest descent until we reach the bottom of the hill. We then repeat this process over and over until we reach a minimum.