Some helpful screenshots of the musician side of Planning Center (descriptions/instructions below each screen shot).
Here's what you should see in your email. Please accept or decline, and click "view plan" to see the week's music.
This is what the plan of the week's music looks like. The circled section above shows the attachments each song has, which is where you can find lead sheets, chord charts, and audio files or links.
Scroll over a particular number in the attachments column to see what files are available.
If you scroll onto the audio attachment (indicated by its file extension), a small speaker will appear. Click on the speaker to open an embedded audio player and hear the song. Alternatively, if you click on any attachment name you can download the attachment to wherever your downloads folder is.
Here's what the embedded audio player looks like, along with its controls.