css js and google font enqueue

first, create a folder inc and inside create a folder enqueue.php

then in functions.php require this  enqueue.php

require_once(get_template_directory().'/inc/enqueue.php');

in enqueue.php file wrire  for enqueue style and css

<?php 

function function_name(){
wp_enqueue_style( 'unique id', get_stylesheet_uri() );

wp_enqueue_style('gfonts',cinthia_fonts_url() ,array(),'1.0.0','all');
wp_enqueue_style('id unique',get_template_directory_uri().'/file link',array(),'version','all');

// also you can add

wp_enqueue_style("'id unique",get_theme_file_uri("/assets/stylesheets/main.css"),null,"version");

//link add

wp_enqueue_style("hexa-font2","https://fonts.googleapis.com/css?family=Playfair+Display:400,400i,700,700i");

wp_enqueue_script('unique id',get_template_directory_uri().'/file link',array('jquery'),version','true');

}

add_action('wp_enqueue_scripts','function_name');

this is google font link 
'https://fonts.googleapis.com/css?family=Open+Sans:300i,400,400i,600,700,800%7CMontserrat:200,300,400,500,600,700,800,900',array(),'1.0.0','all');

//Google fonts to WordPress themes

function cinthia_fonts_url() {
$fonts_url = '';
$OpenSans = _x( 'on', 'Open Sans font: on or off', 'theme-slug' );
$MontSerrat = _x( 'on', 'Open Sans font: on or off', 'theme-slug' );


if ( 'off' !== $OpenSans || 'off' !== $MontSerrat ) {
$font_families = array();

if ( 'off' !== $OpenSans ) {
$font_families[] = 'Open+Sans:300i,400,400i,600,700,800%7C';
}

if ( 'off' !== $MontSerrat ) {
$font_families[] = 'Montserrat:200,300,400,500,600,700,800,900';
}


$query_args = array(
'family' =>  urlencode( implode( '|', $font_families ) ),
'subset' =>  urlencode( 'cyrillic-ext,cyrillic,vietnamese,latin-ext ,latin,greek-ext,greek'),
);

$fonts_url = add_query_arg( $query_args, 'https://fonts.googleapis.com/css' );



 }
return esc_url_raw( $fonts_url);

}

//Adding Google fonts to the editor

function cinthia_editor_styles() {
$OpenSans = (array('editor-style.cs','//fonts.googleapis.com/css?family=Open+Sans:300i,400,400i,600,700,800%7C'));
$MontSerrat = (array('editor-style.cs','//fonts.googleapis.com/css?family=Montserrat:200,300,400,500,600,700,800,900'));

add_editor_style( $OpenSans , $MontSerrat);
}
add_action( 'after_setup_theme', 'cinthia_editor_styles' );

//Adding fonts to the Custom Header screen

function cinthia_custom_header_fonts() {
wp_enqueue_style( 'OpenSans-fonts', '//fonts.googleapis.com/css?family=Open+Sans:300i,400,400i,600,700,800%7C', array(), null );
wp_enqueue_style( 'OpenSans-fonts', '//fonts.googleapis.com/css?family=Montserrat:200,300,400,500,600,700,800,900', array(), null );
}
add_action( 'admin_print_styles-appearance_page_custom-header', 'cinthia_custom_header_fonts' );


for more information visit about google fonts :
 https://themeshaper.com/2014/08/13/how-to-add-google-fonts-to-wordpress-themes/