For the purposes of this article, we're assuming that 'you' are a parent!
You should install the Habyts app on any devices your kids use, including any that you share with them. So the family PC or shared iPad should definitely have Habyts installed.
If you don't share your device with your kids then it's not strictly necessary to install Habyts. For example, if you're the only person to use your phone, you can sign in to your parent dashboard through your web browser, such as Safari or Chrome (just go to www.habyts.com and click 'Sign In').
However, there are benefits to installing the Habyts app on your own device. You'll get notifications (such as if you need to approve a Task that your child has completed); it's also easier to click the Habyts app to open the parent dashboard from your home screen. Remember that if you do install the app, your device becomes locked down until you sign in as the parent!
If you do decide to install the Habyts app on your own device, you do it in exactly the same way as on your kids' devices, but sign in as yourself (and click 'remember me' so you don't have to keep signing in with your password!).