> 1. Just wanna know does this `if(count($rows) == 1` mean the query returns true or false? I mean if it returned something (a user name exsist) than 1 otherwise 0?

`count($rows)` does what it sounds like it is doing : it counts the number of rows returned by the query. If that number equals 1, this conditional expression evaluates to true.

It's worth noting that, if you have set things up correctly, the number of rows returned should never be greater than 1.

> 2. why are we initializing `$row = $row[0]`? what if there were two same usernames? We wont be able to check the second one.... and if there were only one such username than still why the need to initialize it to 0? or did I understood something wrong?

You can't have two users with the same username in your database. Think about it -- how would you be able to tell them apart?

More importantly, you are _not_ setting `$row = $row[0]`. What you are _actually_ doing is:

    $row = $rows[0]

The `CS50::query()` does not just return a row of data; it returns an _array of rows_. In this case, it is only returning one row, but it will still return that row as an _array with only one element_. To index This is a fine point, but one that can trip you up if you're not careful.

> 3. How would this `redirect("/");` redirect to portfolio?

It redirects to `/` which is the Apache2 server's root directory. There it finds and executes `index.php`, which should render a different View if the user is logged in.