In statistics how do you know when to reject the null hypthesis or when to say fail to reject?

Also in Linear Correlation how do you know when to do the


y head=a+bx equation or when to give the mean of y?

In statistics how do you know when to reject the null hypthesis or when to say fail to reject?
you reject your null when your P-value is less than a certain alpha level that you specify.





Hypothetically your P-value is .04923534635, you can reject your null at alpha = .05 but not at alpha = .01





if you are asked for the equation of the least squares regression line, you give the equation:


y = a + bx