You can use this tool to create a favicon https://tools.dynamicdrive.com/favicon/ .
For the favicon to show you will have to upload favicon.ico in the root of your hosting account, the same folder as wp-config.php, then edit the header.php of the theme you are using. Just insert this somewhere before </head> tag.
<link rel="shortcut icon" href="/favicon.ico">
If you are not very comfortable editing php files then use this plugin https://www.digitalramble.com/favicon-manager-wordpress-plugin/
