Sometimes Aurora can't be seen with the naked eyes because its activity is just too low. In that case, you can still see it through your camera.
During the low Aurora, its colour, as visible to our eyes, is grey and if the sky has some clouds you can miss it as everything looks the same.
In that case, just take a photo with long exposure and if you can see green colour on the photo then it's not a cloud it's the Northern Lights.
Usually, photos of the Northern Lights which you can see on the internet are made by professional photographers and are edited which is the reason why the Northern Lights look a bit different in the reality.
The reason is that your eyes see the show in real-time but the camera collects light for several seconds before the photo is made.
Photos look usually better then what you can see in reality but nothing compares to experiencing it under the northern sky with our own eyes.
Nowadays you are already able to make a decent Northern Lights photo with just a phone.
Don't forget to bring a tripod as one photo takes several seconds and the phone has to be completely still in order to accomplish stunning sharp photo.
The photo from a phone won't be as amazing as from a professional camera but it will be still a nice memory of the night you will never forget.