Welcome to Android Central! I moved this from the Introductions forum to the Ask A Question forum, since it's not really an intro.
Which phone do you have? The appearance of that number makes it look like a real-time data transfer speed indicator (that's usually what the up/down arrows indicate). Not sure if this is a built-in feature of whatever phone you have, or if it's a 3rd party app. It'll help to know which phone you have.