What stops foreign residents using Ttareungi is rarely the cycling. It is signing up. Some registration routes will not complete without a Korean phone number, and people usually discover this after installing the app rather than before.
Check which registration route applies to you
Ttareungi is the public bicycle service run by the Seoul Metropolitan Government. Install the app by searching for 서울 자전거 따릉이 on Google Play or the App Store. The official app separates member, non-member and foreign visitor routes, and identity verification and accepted payment cards differ between them. Do not assume an overseas card works on every route. If you do not have a Korean phone number, activating a Korean SIM first, or looking into the short-term passes aimed at visitors, is faster than fighting the registration screen. English guidance is available on the official site at bikeseoul.com.
Renting and returning
Use the map in the app to find a nearby dock and see how many bicycles remain, then enter the bicycle number or scan the QR code to release the lock. To return, put the bicycle back into an official dock, close the locking device, and confirm the return in the app. Leaving it anywhere else can leave the fare running or result in a penalty. If you need to stop briefly along the way, use the temporary lock function in the app rather than ending the rental.
Do not misread the pass
Before paying, check the current price, the per-rental time limit, the conditions for repeat rentals, and the excess charge as four separate things. One misunderstanding is common enough to be worth stating plainly: a one-hour pass does not mean you can ride continuously all day. Exceeding the per-rental limit triggers an excess charge, and how often you may re-rent varies between passes.
Helmets and road rules
Under the Road Traffic Act, wearing a helmet is a legal requirement for cyclists. Note the distinction that trips people up: the absence of a fine for not wearing one is not the same as there being no legal obligation. Bicycles are subject to the same traffic rules as vehicles. Except where the law provides an exception, riding on ordinary pavements is not permitted, and in pedestrian-only sections you should dismount and walk the bicycle. Checking permitted routes and return docks before you set off is what makes the system genuinely useful for stretches the subway does not reach, such as the Han River cycle paths or the Cheonggyecheon walkway.
Shared electric kickboards are classified as personal mobility devices, and their licensing and penalty rules are entirely different from those for bicycles. Those rules, along with what to check with each operator, are covered in the Ttareungi and shared kickboard guide on the WeBring blog.