Install Google Fonts

https://fonts.google.com/

Add to HTML <Head>

Single font family:

<link rel=”preconnect” href=”https://fonts.googleapis.com”>
<link rel=”preconnect” href=”https://fonts.gstatic.com” crossorigin>
<link href=”https://fonts.googleapis.com/css2?family=Montserrat:wght@100;200;400;800&display=swap” rel=”stylesheet”>

Multiple font families:

<link href=”https://fonts.googleapis.com/css2?family=Arimo&family=Montserrat&display=swap” rel=”stylesheet”>

Style reference:

font-family: ‘Oswald’, Helvetica, Arial, serif;

WordPress

<Head> is in header.php