When it comes to connecting your smartphone to your car, the best advice is to check in your owner’s manual. Car manufacturers do not tend to use the same system across brands, so the method of connecting your phone to your car can vary from one car to another.
If you are trying to connect via Bluetooth, the cars infotainment display will typically have an option in settings for connecting a new Bluetooth device. Make sure that your phone’s Bluetooth setting is turned on so the car can find the signal. Some cars will let you specify if you want the car to access just music, or also calls and messaging. Other cars will require access to everything. Some cars will have different audio settings so that anything playing via Bluetooth only plays through the stereo's front speakers. If you want to change the settings, you may need to consult your owner's manual.
More and more automakers are recognizing how complicated it can be for people to connect to different cars, so a lot of brands have started using Android Auto or Apple CarPlay to the cars on-board apps. These applications allow you to access limited apps from your phone via the cars built-in display. These apps are designed to be hands-free, meaning they only work with a limited number of apps, such as maps or messaging. But it also means that once your phone is connected to the car, you won’t have to touch your phone to access these apps.
If you are just looking to play music from your phone through the car stereo, you may see if your car comes with an auxiliary port, often referred to as an AUX port. All you need is a specific cord that connects the car to your phone via the headphone port. Likewise, if you find yourself in a car that is old enough to have a cassette tape deck, you can connect your phone and play music via a tape adapter. Like the AUX cord, these will only work if your phone has a headphone port - but you won’t have to worry about flipping tape sides or rewinding the cassette.
If you end up in a car that doesn't have any of these stereo features - just an old-fashioned radio and maybe a CD player - you can see about purchasing an FM modulator. This is a wireless device that connects to your phone via Bluetooth and/or an AUX cable, and emits a low-powered FM station that you can pick up on the radio. While primarily for music, some of these devices even allow for hands-free calling through the car stereo.