As you browse, your web browser saves some information about the website on your computer. This helps with faster access as it eliminates the need to to download some resources again (such as images, logo's etc.), as you visit the same website over and over. This is called browser cache. Sometimes this cache can cause problems leading to degraded performance as you visit the web page. That's when you need to clear your browser cache.

Information about clearing cache from most major browsers is available here - https://kinsta.com/knowledgebase/how-to-clear-browser-cache/