An icon is a small picture used to represent an action, object, or idea. It is like a road sign: a familiar shape can give you a quick clue without using many words.
For example, a magnifying glass is often used for search. But not every symbol is familiar to everyone, so a short word beside it can make its purpose clearer.
Choose a symbol that matches what it does, and keep it consistent wherever it appears. If an icon is the only control label, make sure its meaning is explained for people using a screen reader too.