I want to know which of the following sentence is correct.
The ship is sailing on the sea.
The ship is sailing in the sea.
Also help me with one more question.
What is the difference between 'in' and 'inside'.
In and inside can be used in the same sense.
The ice cube in/inside the glass.
In other senses, "in" can have the sense of movement into something while "inside" implies being surrounded.
He walked in the door. (not inside)
Pope of the Dictionary.com Forum