Alejandro - In most cases (assuming you are investing in publicly traded companies) you can perform an internet search which will provide you with links to the company web sites as well as the thoughts and comments of others on that company. As you mention the American Funds I will assume that at least a portion of your portfolio consists of mutual funds. In that case any single fund may invest in anywhere from 10 to 1,000 companies, or more. When investing in a fund you are delegating the individual company research and investing to the fund managers. In this case it is important to understand why you have invested in that particular fund and how it fits into your overall portfolio allocation.
Alejandro, I suggest that you talk with a person who has been trained to understand balance sheets, income statements and evaluation methods. A Chartered Financial Analysis is well trained in the above and can help you with your "looking for more information."