Hi all sifu please guide me on this stock concept. i have read quite some basic stock trading books but i haven't started playing yet and is still confused. There are 2 main questions that I still don't understand about calculation of stock trading

1) Those books at first talk about the magic of compounding and say why it is important all that. Then they will give an example of calculation with different ROI and say why it is important to have high ROI. For example this one.

"If you invest $2k yearly for 35 years with an interest rate of 12%. At the end of 35 years you will have $1.08m."

My question is about the 'interest rate 12%'. Is it possible to know the % of interest for this particular stock? I mean is the interest rate % constant all the time? What if there is any economic downturn like the 2008 crisis will it still give me 12% every time? The book mentions like the 12% interest is consistent throughout the 35 years without any changes.

2) Using the above example, it says 'invest $2k yearly for 35 years'. Does that mean every year I use $2k to buy that particular stock for 35 years? Which means I will spend $70000 ($2k x 35 years) throughout my 35 years life? Does that also mean I have more and more of that company's stock as time passes by?