I’m using Windows 8, I have a recording from a wedding in which you can hear a lot of people mumbling in the background and was wondering if anyone could help me silence their sound.
I watched a video tutorial on Youtube, but it said to use certain effects that were unclickable on my version (They were grayed out)
Any help would be very much appreciated!
effects that were unclickable on my version (They were grayed out)
The effects will be greyed-out while playing the file. Make sure playback is stopped (or never started) before applying the effects.
You can try the [u]Noise Removal[/u] effect.
But if the mumbling is loud, “the cure may be worse than the disease”. Noise Removal works best when you have a constant low-level sound… i.e. It works best when you don’t really need it. 
Professionals with access to the latest pro software still record in soundproof studios with good equipment and careful microphone placement, etc. “On location” movie dialog is re-recorded in the studio.
If this is a video and some of the audio is unintelligible, consider subtitles. If the noise is actually annoying or distracting, sometimes it’s better to lower the overall volume and add subtitles.