Can help me with these questions its for my Macroeconomics class to help me review.

The chapter is 5, and its called "The Full Employment"

I having difficulties understanding the topic so I need help.

1. How do competitive markets with flexible wages and prices ensure that labor is always fully employed? What induces firms to create just the right number of additional jobs to match an increase in the number of workers? 2. Describe the effects of changes in labor supply on equi- librium real wages and potential GDP (full-employment level of output). 3. What determines the economy's productive capac- ity or aggregate supply or potential GDP? How does aggregate supply increase when labor supply increases? 4. What is investment? Why does investment decrease when the real interest rate increases? What role do expectations play in investment? 5. What determines the level of saving? Explain why, if taxes are fixed, disposable income in a full-employment economy is fixed. Explain why saving may not be very sensitive to the real interest rate. 6. How are leakages and injections balanced? Why will demand and supply in the product market be equal if leakages and injections are equal