Buying and selling is a very broad topic that likely refers to buying and selling stocks. One can learn about buying and selling stocks from many sources including Investopedia and About - Stocks.
In purchasing stocks, you buy a piece of ownership in the company. The buying and selling of stocks can occur with a stock broker or directly from the company.
No. Buying and selling stocks is normal and acceptable. There is a higher tax rate on money gained by selling stocks owned a short time. There is a very small SEC fee added to stock sales.
The main disadvantage of buying penny stocks is that the value of the stocks fluctuate enormously on a day to day basis. Penny stocks may also be very hard to sell once you own them. To benefit from penny stocks, one must be very knowledgeable and experienced with buying and selling stocks, so penny stocks are not for first time buyers.
Short selling stocks is risky because there are no guarantees of what the market share will be after the sell. The return rate could be high or low, depending on if the stocks fell as predicted.
At the federal level it's the Securities and Exchange Commission (SEC). States also have their own regulatory authorities.
By selling shares and stocks to their investors
Through the selling of stocks "Investors"
by selling bonds and issuing stocks...