I've said it before and I'll say it here again: You don't have to be rich to invest in the stock market. There isn't a secret that only a few investors know to be successful at investing either. In order to build and grow a market-beating portfolio, what you do need is patience, time, and a well-outlined investing strategy.

Here at The Motley Fool, we believe that a long-term investing strategy is the most effective means of building and sustaining wealth through the stock market. When you only invest in excellent companies that you plan to hold onto for many years, you'll not only have an easier time riding out the ups and downs of the market, but you can continue to consistently buy more great stocks no matter what the market is doing. 

If you have $600 to invest in the market right now, these are two companies that you should consider adding to your buy basket. 

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1. Pfizer

This is a healthcare stock that needs no introduction. Pfizer's (PFE -1.96%) name has been splashed across the headlines over the past 18 months as it emerged a clear winner in the coronavirus vaccine race along with its German partner BioNTech. In August, Pfizer & BioNTech's coronavirus vaccine, which is being marketed under the name Comirnaty, was the very first to win full approval from the Food and Drug Administration.

In late September the companies were also the first to win an emergency use authorization from the FDA for a booster dose of their vaccine in specific populations. The vaccine partners also recently submitted pivotal trial data to the regulatory authority signaling that they are one step closer to requesting an EUA for the vaccine for children between the ages of five and 12.

By now, it's no secret that the maker of Advil, Lyrica, Viagra, and Eliquis is expecting to generate significant revenue in the tens of billions of dollars from the coronavirus vaccine just in 2021, which will likely only be compounded in the years ahead. But unlike some of the other players in the coronavirus vaccine race that were relative unknowns to the public before the pandemic began, Pfizer has been in business for well over a century, and has a tremendous collection of household-name brands in its product portfolio.

The company also has an impressive product pipeline featuring 100 pharmaceutical drug candidates at the time of this writing. Pfizer's future definitely looks brighter with the addition of Comirnaty to its portfolio, but its proven resilience, brand authority, and diverse portfolio of consistently top-selling products are also what make it such a compelling long-term investment. 

Revenue grew 92% in the most recent quarter, and net income surging 59% year-over-year. Excluding COVID-19 vaccine sales of $7.8 billion, revenue grew 10% which suggests Pfizer is going from strength to strength. While Pfizer's share price growth has historically been more on the modest side, the stock's 3.7% dividend yield is a key buying point for investors to consider. 

2. Veeva Systems 

Veeva Systems (VEEV -2.38%) is another stock from the healthcare universe, but with something of a twist. The company broadly operates in the extremely high-growth and lucrative world of cloud computing. However, it has specifically geared its services toward life sciences and pharmaceutical companies.

From helping healthcare companies of all sizes streamline their regulatory compliance process to offering business consulting services to commercial analytics to a comprehensive suite of clinical, medical, and other cloud-based solutions, Veeva Systems does it all. 

And with major names in in the healthcare industry like Bayer and Biogen numbered among the growing customer base that rely on its platforms and services to help manage their business operations, Veeva Systems has clearly succeeded in its chosen niche. 

Veeva Systems isn't just growing its revenue at a extremely healthy pace pace (29% year-over-year in the most recent quarter), it's also very profitable. Its net income popped 16% year-over-year in the second quarter, while operating income surged 38% from the year-ago quarter. And with total current assets of $3.4 billion ($1.1 billion of which are cash and cash equivalents) compared to total current liabilities of just about $663 million, Veeva's growth isn't hindering its ability to meet its liabilities or increase its available cash. 

The stock has risen by a more than 530% since it became publicly traded eight years ago. Veeva Systems has plenty of room to run in the space it's carved for itself in the global cloud computing industry, and investors who buy in now could reap the rewards of that trip skyward.