Cortana was able to set reminders, recognize natural voice without the requirement for keyboard input, and answer questions using information from the Bing search engine. Searches using Windows 10 are made only with the Microsoft Bing search engine, and all links will open with Microsoft Edge, except when a screen reader such as Narrator was being used, where the links will open in Internet Explorer. Windows Phone 8.1's universal Bing SmartSearch features were incorporated into Cortana, which replaced the previous Bing Search app, which was activated when a user presses the "Search" button on their device. Cortana includes a music recognition service. Cortana was able to simulate rolling dice and flipping a coin. Cortana's "Concert Watch" monitored Bing searches to determine the bands or musicians that interest the user. It integrates with the Microsoft Band watch band for Windows Phone devices if connected via Bluetooth, it was able to make reminders and phone notifications.

Since the Lumia Denim mobile phone series, launched in October 2014, active listening was added to Cortana enabling it to be invoked with the phrase: "Hey Cortana". It was able to then be controlled as usual. Some devices from the United Kingdom by O2 received the Lumia Denim update without the feature, but this was later clarified as a bug and Microsoft has since fixed it.

Cortana integrated with services such as Foursquare to provide restaurant and local attraction recommendations and LIFX to control smart light bulbs.
Cortana stored personal information such as interests, location data, reminders, and contacts in the "Notebook". It was able to draw upon and add to this data to learn a user's specific patterns and behaviors. Users were able to view and specify what information was collected to allow some control over privacy, said to be "a level of control that goes beyond comparable assistants". Users were able to delete information from the "Notebook".
Cortana had a built-in system of reminders, which were able to, for example, be associated with a specific contact; Cortana would then remind a user when in communication with that contact, possibly at a specific time or when the phone was in a specific location. Originally, these reminders were specific to the device Cortana was installed on but starting on February 12, 2015, Cortana synchronized reminders across devices.
Most versions of Cortana took the form of two nested circles, which were animated to indicate activities such as searching or talking. The main color scheme would include a black or white background and shades of blue for the respective circles.
Cortana on Windows mobile and Android were capable of capturing device notifications and sending them to a Windows 10 device. This allowed a computer user to view notifications from their phone in the Windows 10 Action Center. The feature was announced in early 2016 and released later in the year.
Cortana had a "do-not-disturb" mode in which users were able to specify "quiet hours", as was available for Windows Phone 8.1 users. Users were able to change the settings so that Cortana calls users by their names or nicknames. It also had a library of "Easter Eggs", pre-determined remarks.

When asked for a prediction, Cortana correctly predicted the winners of the first 14 matches of the football 2014 FIFA World Cup knockout stage, including the semi-finals, before it incorrectly picked Brazil over the Netherlands in the third pl…

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Microsoft integrated Cortana into numerous products such as Microsoft Edge. Microsoft's Cortana assistant was deeply integrated into the browser. Cortana was able to find opening hours when on restaurant sites, show retail coupons for websites, or show weather information in the address bar. At the Worldwide Partners Conference 2015 Microsoft demonstrated Cortana integration with products such as GigJam. Conversely, Microsoft announced in late April 2016 that it would block anything other than Bing and Edge from being used to complete Cortana searches, again raising questions of anti-competitive practices by the company.

Microsoft's "Windows in the car" concept included Cortana. The concept makes it possible for drivers to make restaurant reservations and see places before they go there.

Cortana was able to integrate with third-party apps on Windows 10 or directly through the service. Starting in late 2016, Cortana integrated with Microsoft's Wunderlist service, allowing Cortana to add and act on reminders.

At Microsoft's Build 2017 conference, Microsoft announced that Cortana would get a consumer third-party skills capability, similar to that in Amazon Alexa.

On February 16, 2018, Microsoft announced connected home skills were added for Ecobee, Honeywell Lyric, Honeywell Total Connect Comfort, LIFX, TP-Link Kasa, and Geeni, as well as support for IFTTT. At Microsoft's Ignite 2018 conference, Microsoft announced an Technology Adopters Program that Enterprises could build skills that could be developed and deployed into Azure tenants, accessible by organizational units or security groups.

Cortana indexed and stored user information. Cortana could be disabled; this would cause Windows search to search Bing as well as the local computer, but that could also be disabled. Turning Cortana off did not in itself delete user data stored on Microsoft's servers, but data was able to be deleted by user action. Microsoft was further criticized for requests to Bing's website for a file called "threshold.appcache", which contained Cortana's information through searches made through the Start Menu, even when Cortana was disabled on Windows 10.

As of April 2014 , Cortana was disabled for users aged under 13 years.