Aircrack-ng is a tool that can be used to hack Wi-Fi networks and recover their passwords. In order to do this, you will often need an external wireless card that supports packet injection.
Each operating system is different, meaning some have more limitations than other. Linux for example, is capable of injection and listening to network traffic. Windows is only capable of listening to the traffic which is a software limitation.
Picking the right card is dependent on personal requirements, such as what interface to use and much range you need. USB is the most common, and can be used even when mounted into a virtual machine. Each card also has two manufacturers, the brand of the card and the chipset maker. Brands can include Linksys, TP-Link, Belkin etc, which the two biggest chipset makers are Atheros and Realtek.
The chipset manufacturer is crucial to know because it is what lets you know if your operating system is supported and there are proper drivers for it.
Here is a list of cards that are supported and have been tested to work. – https://www.aircrack-ng.org/doku.php?id=compatibility_drivers#which_is_the_best_card_to_buy
Personally I have the TP-Link TL-WN722N, which is very popular and only about 10-15 dollars, making it very accessible and can help you improve your skills greatly. – https://www.amazon.com/TP-Link-N150-Wireless-Adapter-TL-WN722N/dp/B002SZEOLG
Using these cards in a Linux Virtualbox environment is also very important, as all you have to do is enable it in the USB filter settings.
As you can see, the Wi-Fi card you select is very important, as it extends the functionality and features you have access to in your penetration testing environment. Always make sure to see if it is compatible before buying, and don’t do anything illegal with it.