how to use the "the alter table statement "

the alter table statement is used to modify ,add ,delete columns in an existing table
1 to add a column in a table ,use the following syntax:
alter table table_name add column_name datatype
2 to delete a column in a table ,use the following syntax
alter table table_name drop column column_name
3 to change the data type of a column in a table ,use the folloing
alter table table_name modify column_name datatype;