you just need a <input type="file"/ name="myFile"> input field and then an autoglobal array $_FILES['myFile'] will be available. This array has a second dimension with following keys:
name - the name of the uploaded file with extension
type - the filetype (
mime type)
size - amount of bytes of the file
tmp_name - absolute path to the temporary file (its name is random)
The rest (storing to a folder, uploading to a database, showing the file) goes to your imagination.
If you need some more help, just tell us.