For e.g. In order to determine whether the humidity in Mumbai is in the same range as that of Pune, the null hypothesis could be the humidity levels in the two cities are same. Alternative hypothesis could be that the humidity levels in the two cities are not the same.
The alternative hypothesis could be:
Point Hypothesis: When the alternative hypothesis points at one particular value
One-tailed directional: when the region of rejection lies on only one side of the distribution
Two-tailed directional: When the region of rejection lies on both sides of the distribution
Non-directional: It is not concerned with any direction but only with the rejection of the null hypothesis
If the null hypothesis is not true, it does not mean that the alternate hypothesis is definitely true. It merely indicates a possibility given the possible range of error that the alternative hypothesis may hold true.