It all depends on whether the bottle is open or closed, and how long you want to store it.
If you want to store your champagne for several years, the ideal is to store it in a wine cellar at a constant temperature of 14°C. It's not a problem if the temperature varies between 10°C in winter and 20°C in winter, but the variation must be as gentle and slow as possible. Other important points: there must be absolutely no direct light on the bottles (otherwise you risk giving them the famous "taste of light") and the humidity (humidity level) must be around 70%. (This is also not a problem if you store your bottles in a cellar at 80% humidity.)
If you want to store your champagne for a few weeks to a few months, it's very easy: put it in the refrigerator, ideally lying down. If you've opened a bottle and it's still unfinished, you can simply recork it with a stopper and place it upright in the refrigerator. The champagne's bubbles and freshness will last for 48 hours.
In any case, avoid hot, humid, and brightly lit areas!
You probably have other questions; here are our answers in the following links:
How to properly chill a bottle?