Confusion between Pronouns

Hi Madhavi Latha,

It is just two different ways of saying the same thing to express possession.

You can say -

Cet ordinateur, c'est le mien 

or

Cet ordinateur, il est à moi.

Because of the preposition à, you use a different pronoun, the same ones used after 'chez'', sometimes called 'stress pronouns'. If not sure take a look at the following Kwiziq lesson -

https://french.kwiziq.com/revision/grammar/common-uses-of-moi-toi-lui-elle-nous-vous-eux-elles-disjunctivestress-pronouns

So to recap, if you say -

Cet ordinateur est le mien = This computer is mine

Cet ordinateur est à moi = This computer belongs to me ( = is mine)

Hope this helps!