How to make a website with two types of logins , Sellers and buyers?

Use a single login, and tag each user as either a buyer or a seller using user meta

e.g. lets use a user meta field called shireefs_login_tag

To set the tag:

update_user_meta( $user_id, 'shireefs_login_tag', 'buyer' );

To read the tag:

get_user_meta( $user_id, 'shireefs_login_tag', true );

To redirect on login:

function my_login_redirect( $redirect_to, $request, $user ) {
    if ( !empty( $redirect_to ) {
        return $redirect_to; // dont mess with existing redirects
    }
    //is there a user to check?
    if ( isset( $user->roles ) && is_array( $user->roles ) ) {
        //check for admins
        $login_tag = get_user_meta( $user->ID, 'shireefs_login_tag', true );
        if ( 'buyer' === $login_tag ) {
            return home_url( 'buyers' ); // example.com/buyers
        } else if ( 'seller' === $login_tag ) {
            return home_url( 'sellers' ); // example.com/sellers
        } else {
            return home_url( 'choose' ); // example.com/choose, we dont know if they're a buyer or a seller yet
        }
    } else {
        return $redirect_to;
    }
}

add_filter( 'login_redirect', 'my_login_redirect', 10, 3 );

With this information you now know how to:

• store if a user is a buyer or a seller
• retrieve that information so that you can do things with it
• redirect users to a location based on that info when they log in

Everything else can be built off of those