How could I make and display a timer counting up?

Im making a game meant for speedrunning, and I want to know how i can implement a timer in my game. Help please?

Check Unity Tutorials,
Short Answer:
Make a Canvas, Add a Text, Make a script: then do this:
Text Timer;
int GameTime = 0;

public void Timer(){
Timer.text = GameTime;

void Update(){
GameTime = GameTime + Time.deltaTime;