how to add previous and next link for the posts?

Here’s a good place to start:

As you will see, keeping the links to posts of the same category is as simple as setting an argument in the function.

I would give an example but there are really good examples on the pages linked above.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)