Well I watch a lot of video tutorials but the admob ads doesn't show on the exported game, I've tried everything but nothing works for me.
If I remember this correctly, Admob Ads won't show up, if the registered Google Play Store e-mail address
is the same as the one used for the Google Developer Console. (?)
Admob Ads should generally work if you export your game and install it in "unsafe" mode on your device.
Just remember to enable "Test Mode", else you will be blocked by Google Admob for clicking/watching your own ads.
If they still don't show up using the unsafe way, you can be sure that the problem is caused by your side of things.
(It might also take a couple of days after release, in my case it took about 3 days until watching ads was possible.)