Dear Ram,
Leaves are mainly of two types: Statutory and Non-statutory.
1. Statutory leaves are those leaves that ought to be given to all employees as per the law of the land applicable to the class of the employee.
2. Non-statutory leaves are those leaves which the company gives to its employees over and above the statutory compulsions. Both are further classified as Annual leaves and Earned leaves.
1. Annual leaves are credited to the employee's account immediately upon his/her joining, prorated for the remaining year.
2. Earned leaves are credited based on his service or actual attendance in the previous year (or as the policy may be).
Non-statutory leaves are classified and given by every organization to its employees as per their policy and practice, and the number of days varies from company to company. For Statutory leaves, please refer to relevant laws such as the Factories Act, Maternity Benefit Act, etc.
Hope this helps you clear some of your doubts, Ram.
Prashant