critical value and test static

I believe if critical value that is obtained from t-static or z-statistic is less than test statistic , null hypothesis is rejected? Am I correct? Could you please explain the meaning of comparing these two values. Appreciate your help.

That’s right, if you compare all your values in absolute numbers. The critical value is the one you would expect the maximum one for your sample, if H0 is true (with an prob. of 1-alpha %). The test statistic is the real value you obtain for your sample.