Many symbols and special characters are required while developing a web page in html, but as we know that sometimes the use of characters directly may interfere with the actual html code which have certain characters reserved and also certain characters being not available on keyboard. Thus, to avoid the conflict and at same time to be able to use different symbols in our code w3 org provides us with 'Character Entities'.
Character Entities are predefined with 'Entity Name' - &entity_name; and 'Entity Number' - &entity_number; so we need to use either of the two for the required symbol to be rendered on our page.
The list of few Character Entities can be found at https://dev.w3.org/html5/html-author/charref
A simple example with the use of character entity for 'magnifying glass' :
<input type="text" placeholder=" 🔍 Search"/>
which renders as