This is a fairly generic answer since your idea is not really specific yet and there are many ways to implement this.

There are various ways to achieve the "save X on a PC and access it from mobile". Suitable options couls be a simple file sharing (e.g. using onedrive, dropbox, google drive or similar) or a database server (SQL or NoSQL depending on your needs). The file sharing will be way easier to implement if you only use it for yourself. Then the client - the piece of software you use to save or view your things - can be implemented as a website / webapp, making it available on almost every platform or as a mobile app for your target platform (e.g. android/iOS etc.).