Advanced Custom Fields is a very powerful custom field plugins, allowing you to add a variety of custom field types, such as Image, Checkbox, File, Text, Select, True / False, Link, Textarea, and so on, can be integrated into one or more panels, support the export field XML or PHP code. Advanced Custom Fields can be also integrated into themes or plugins.
Search Advanced Fields Custom and install it in the admin panel, or download Advanced Custom Fields. Enable Advanced Custom Fields, Click the “add fields”, fill in the relevant information and choice, the field name must be English, strigula, underscores, no spaces, Then save the publication. More usage, you can look at the official tutorial: https://www.advancedcustomfields.com/resources/
If you know a little PHP code, with the help of Advanced Custom Fields, you can achieve a very powerful custom field function to enhance your site. If you want to Advanced Custom Fields integrated into your theme or plugin, wordpress best plugin advise you to view their official tutorial.