Base64 is a way to represent files as text. By using text instead of the original file it can be easier to place it on a webpage or to share it with other people. For example, HTML tags accept base64 data in their src fields. The base64 text contains the contents of the file but anything else such as the filename will be lost. The size of base64 output is generally a lot larger than the size of the original file. It makes sense to only use base64 text when you really need it.
When you use this converter the file you use will stay in your browser; the file is not sent anywhere. Note that if you try to convert a very large file, your browser may hang because your device cannot handle converting a file that large.
After you have selected a file from your computer, the base64 representation will be shown here. If you select a very large file your browser or browser tab may crash.