TD Ameritrade focused its 2019 development efforts on its most active clients, who are mobile-first – and in many cases, mobile-only. TD Ameritrade’s thinkorswim mobile platform has extensive features for active traders and investors alike. The workflow for options, stocks, and futures is intuitive and powerful. You’ll find lots of bells and whistles that make the mobile app a complete solution for most trading purposes, including streaming real-time data and the ability to trade from charts. The regular mobile platform is almost identical in features to the website, so it’s an easy transition. TD Ameritrade clients can trade all asset classes offered by the firm on the mobile apps.
The IBRK Lite plan enables affordable investing with no commissions and no account minimums on its stocks and ETFs. Its Pro plan is for the regular investor, with specific fees based on your investment activity. Research and education are impressive, with its Traders’ Academy offering free courses and several applications designed to help you make better investments. 
A demo account is a great way for beginners to practice trading and test a broker or trading platform without using real money. A demo account is funded with simulated money, so you can try out the broker’s platform features and get familiar with acting on the markets. A warning though – even the best practice platform can’t replicate the pressures that comes with having real money on the line, but it’s a great way to learn the basics and get started with zero risk.
You're probably looking for deals and low prices, but stay away from penny stocks. These stocks are often illiquid, and chances of hitting a jackpot are often bleak. Many stocks trading under $5 a share become de-listed from major stock exchanges and are only tradable over-the-counter (OTC). Unless you see a real opportunity and have done your research, stay clear of these.

As you near retirement, a full-service brokerage firm may make more sense because they can handle the complex "stuff" like managing your wealth in a tax-efficient way, or setting up a trust to pass wealth on to the next generation, and so on. At this point, it may be advantageous to pay 0.50%-1% of your assets in fees each year for advice and access to a certified public accountant who can help you with the nitty-gritty details that are more important as you start making withdrawals (rather than contributions) from your retirement accounts.
The trading products you can purchase using these platforms can include stocks, commodities, derivatives, bonds etc. which can be traded between the traders on the stock market with intermediates such as investment banks, stock exchanges, brokers and market makers. A communication network is set-up between the various intermediates and the traders, which facilitates proper execution of the whole system.