Critical thinking is the ability to evaluate information instead of accepting it.

For example, when you read a newspaper, a critical thinker examines:

-Who's writing the newspaper?

-What are their biases and objectives?

-What sources do they use for their information?

-Can I trust them to report honestly?

-Who pays the writers? How does the affect their honesty?

-Is this article logical? Are there any logical flaws in it?

-How does this news article compare with other articles by different newspapers?

Everyone does this to some extent. Critical thinking is just having a more organized habit of doing it.

It means to think well using reasons and cheking every detail side by side to give a good answer or explaination.

It means that you think through something to make sure that it is logical and to find any inconsistencies in it before believing it.