The Prompt for File action (v8+) prompts for a selected file or folder and saves the path into a variable.

You can prompt for an existing file or folder, or for a new file or folder.

For a new file or folder, you can specify the default file name.

For an existing file, you can specify the allowed file types with a space or comma separated list of extensions or Uniform Type Specifiers such as public.image.

: Until we can provide a better description, see this macro for an example with screenshots:
MACRO: Prompt for File Action

• Prompt for User Input
• Custom HTML Prompt action
• Prompt With List action
• Get Touch Bar Selection action
• All Actions