In a one-way ANOVA, if the computed F statistic is greater than the critical F value, you may reject the null hypothesis. This suggests that there are significant differences between the means of the groups being compared. More specifically, the null hypothesis typically states that all group means are equal, while the alternative hypothesis suggests that at least one group mean is different. If your F statistic exceeds the critical value derived from the F-distribution (based on your chosen significance level and the degrees of freedom), you can conclude that there is enough evidence to suggest a significant difference among the group means.
After rejecting the null hypothesis, it is often advisable to conduct post-hoc tests (such as Tukey's HSD or Bonferroni) to determine which specific means are significantly different from one another.