maybe think of it like water flowing through pipes:

Apps, websites, videos, and maps are taps that use water.

When you open an app or load a webpage, data flows from the internet to your phone (downloading).

When you send a photo, message, or upload something, data flows from your phone to the internet (uploading).

Your mobile plan gives you a certain amount of water (data).

Some general data sizes

Small image (thumbnail): 50 KB — e.g., 200×200px JPEG thumbnail photo, quick social-media preview.

Single full page of text (plain): 10–50 KB — e.g., one A4 page saved as plain .txt or small Word .docx without images.

Single full page of text (scanned PDF, image): 500 KB–2 MB — e.g., scanned A4 page at moderate resolution saved as PDF.

Normal web page (text + images + CSS + JS): ~10 MB — typical news article with several images and scripts.