What kind of securities should I focus on to build an aggressive growth portfolio?
The first step is to create an emergency fund of the 3-6 months of non-discretionary expenses earmarked for life’s unpredictable circumstances. The next step is to properly position yourself for retirement and other future goals by saving an appropriate amount. I'm going to assume you're already on track with these important financial aspects and the $22K is essentially disposable - you can afford to lose it. If this is not the case, please look into establishing an emergency fund and a retirement fund before choosing to invest aggressively.
Considering you are new to investing; if you also do not have much of an interest in investing, then investing in a low-cost and diversified mutual fund or exchange traded fund (ETF) with prominent exposure to US and world equity can be a good option. Vanguard, along with many other companies, have multiple low-cost investment options in this category. In the process of building capital and as your portfolio grows, a good rule of thumb is to gradually transition from an equity-heavy portfolio to a more conservative fixed income portfolio. Generally, equity is perceived more aggressive than fixed income.
If you are interested in getting more involved with investing than just investing in funds, then you have an ocean of philosophies and options. Some investors may argue that you cannot take on more potential for return (become more aggressive) without taking on more risk. Risk can be defined in many different ways and not every investor can agree on a default definition. Some would call investing in something less diversified than a fund to be adding to your amount of risk, thus being more aggressive. An example of this would be investing in individual stocks. I wouldn't recommend investing in individual stocks unless you possess a strong interest, are very ambitious to learn, and have an adequate source to provide you with the information that you would need to learn the trade.
Depending on which form of investments you choose, and the type of account in which those investments are held, will determine how your taxes will be handled. You could very easily invest in an aggressive mutual fund or ETF inside of a Roth IRA with favorable tax treatment - assuming you qualify for a Roth IRA. Although, a Roth IRA is a retirement account and if you are planning to use this money for something other than retirement, a Roth IRA will most likely not be the best choice. An individual brokerage account can be used for investing purposes other than retirement. If you use an individual brokerage account, you will be taxed annually by the amount of gains you realize inside the account.
Bottom line: the securities you choose to focus on will depend on your anticipated level of involvement and how aggressive you actually want to be. The precautions you should take when considering tax planning will depend upon your goals for investing (as well as many other factors that may require you to meet with a professional CPA depending on how intricate your personal situation is).
This is a very complex question, but I hope that I have helped to get you thinking in the right direction. Best of luck!
Aggressive is a tricky word, but with your very long time horizon, you may want to consider a combination of small cap US stocks as well as emerging market stocks. Both are available thru exchange-traded funds, which tend to be more cost-effective that mutual funds. For tax planning, think in terms of holding periods greater than a year, so you get the benefit of the lower capital gains tax rate.
Adopt a Value Investing mindset when it comes to security selection. Read everything about Warren Buffett and if you have the expertise to properly value a security, then only buy when you can do so at a large discount to fair value.