What do people mean compound interest in Stocks? What does it mean when people say the first million is the hardest?

Question 1) What do people mean compound interest in Stocks? I have invested is mutual funds and individual stocks. I do on occasion see dividends but I don't see compound interest. People swear on how great compound interest is on mutual funds, but I don't see them. Between mutual funds and individual stocks, mutual funds takes the longest to grow and get ROI. Years often just to see 25% in return. I think the growth in mutual funds comes from inflation and the appreciation in stock value, less so "compound interest". So what do people mean with compound interest in stock? Question 2) What does it mean when people say the first million is the hardest? **Edit: folk are skipping this question. Are we just referring to getting to a million in Individual account, or is that a million across all accounts (401K, Roth IRA, HSA, and Individual accounts)?**