I have a "bubble" under my fondant around the sides, I don't expect to be able to fix it but not sure what caused it. Did I work too fast putting the fondant on? Is there too much icing underneath? Anyone know what usually causes this? Also was thinking maybe I didn't let the cake set long enough...? I looks like too much frosting but feels like there's only an air bubble underneath it.

You put too much icing underneath. Always put a light layer and make sure to refridgerate it before the fondant.

If it's just an air bubble, stick a pin in it and you get that air right out! It happens to me occasionally too and I have to "burp" it! LOL! Seriously, I stick the middle of the bubble with a corsage pin and just work the bubble toward the pin.

How long did you let it settle? Did you chill it before you put your fondant on? What kind of icing did you use?

Why can't you fix it? All you have to do is use a pin come in at a slant stick it in and gently work the air out and useyou fondant smoother or your hands.

Okay, I didn't chill it before the fondant. I was never told to do that so I didn't think it was necessary. I used butter cream icing (made with all butter) because that's what I always ice with. However I haven't done any fondant cakes since my cake classes and I did use the class butter cream during class (which was all shortening) but my family hates the stuff. After icing the cake I think I let the cake sit for about 45 mins to an hour...?

I was considering "popping" the bubble but I was afraid I would just make the cake look worse or tear a big hole in it or something. I've heard of people popping little bubbles in the surface of the fondant but this is like a pocket of air underneath...?

I am a newbie also, so take that into consideration when listening to my advice.
I don't have room to refrigerate my cakes before putting on fondant, and I haven't had a problem. And yes, you can just prick it with a pin, and the air bubble goes away! It is pretty cool the way it works. I was upset when I had bubbles in mine also, and figured I couldn't hurt it too bad, so I tried the pin prick thing. You don't even see the pin prick, it just blends into the fondant. I hope this helps.

I always put loads of bc on my cakes. I refrigerate it well prior to covering it with fondant, that way if you need to readjust where you are placing it, it doesnt mess up your bc. If you get air bubbles(they are common) prick it and rub it smooth, you can also put a dab of bc of same color in the hole if needed....Its not too much frosting unless you moved it when covering it was if not chilled and a gob of bc is that bulge rather than air

just be aware that covering a cold cake can lead to its own problems - more air bubbles, condensation. not everyone has this happen, but worth knowing to look out for.
when putting your fondant on, thry to roll it over the cake rather than just drop it on. as u smooth the top, lift the sides to get any air out. then work round and down the cake, hopefully also getting air out.
then if all fails, use the pin prick! but do it sooner rather than later - if your fondant has started to firm up it wont look as good.
xx

If you let your cake settle for a few hours, that could help. If you chill it or as some do stick it in the freezer for about 10 minutes that will help. (won't hurt, because the cake is not frozen or cold to the core) Make sure you get it to "stick" to the buttercream while smoothing it. And if bubbles happen, (and they do!) do the pin thing ASAP or it could get bigger and pop. (had that happen . A little pin prick can be hidden or as Madgeowens suggested, use a little buttercream to fill the hole. HTH