To create an audio file use Audacity which is found under All Programs in the Start menu on your laptop/desktop.
Open the programme and record using the red circle to start, the yellow square to stop and the green triangle to play back.
When you are happy then click File in the top menu then Export.
Check the file type is MP3 and save your file.
Create a New Post.
Select Add Media from the top screen menu.
Click Upload Files and locate your MP3 file.
Then click Insert into Post on the bottom right of the screen e.g.
Click Update (blue publishing button on right screen menu).