The stock market is like a grocery store. In a grocery store, everything is neatly organized in rows and shelves. In the stock market, these are re-named as sectors and market cap. There is a sector for oil and oil related industries. A sector for electronics and then subsectors for consumer electrictronics and industrial electronics. Then electronic suppliers and manufacturers, so on and so forth.
Like a grocery store, there are aisles for baked goods, breads, rolls, pasteries, cookies and cakes. The stock market is no different, just different names and differant ways to buy, sell and invest in it.
Think about investing your own money, learn to play the game, it's not that hard if you rearrange your thinking a little bit.