First there is three items that help an entrepreneur create a business. They need a favorable tax code, capital, and an idea for a product or service. If you wont make a profit because of the tax code you wont open a business. If you can't get any investors, or loans from the bank, chances are you wont have enough money to open the new business. If there is no room in the industry for your product or service, you wont open your company as well. That's the basis of a company.
The economy works in a cycle. You disrupt any part of the cycle it all falls apart. We can start from any part of the cycle and show how it works. I like to start from the business. Lets begin. First if a company has low taxes they will have more money. If a company has more money they will use that extra money to expand their company to make more money. When that company expands they need to hire more workers to work for the company. If more Americans get hired there will be less unemployed Americans, thus having the government spend less money on government services. If more Americans have jobs more Americans are paying taxes which will expand the government's tax base. This would bring more revenue in for the government. If Americans have low taxes, Americans will have more money to spend. If they spend that money extra money, this in return would expand the company's they bought the product or service from and overall expanding the economy.
Lower taxes and basically more capital for Americans and companies is what drives this economy to be great.