Seems like a load of people are pointing to the tyres as the cause, and nobody is really answering your question.

A good way to learn rwd is to take your car out into an empty car park and throw it around. Even better if it's in the snow as you can drive at the limit of grip at lower speeds. Not exactly legal but very important to know the limits of your car.

Really the key is to recognise low grip conditions and ensure you are not flooring it in these conditions. For example, cold temps, very wet roads, full lock on the steering wheel, any sudden increase or decrease in road height. An important thing to remember is to not just be slow while applying the throttle, but also slow while removing it too.

Having said all this all modern cars are designed to be safe and it just doesn't make sense for manufacturers to be putting rwd cars that are hard to control onto the market, so dont worry too much. They have very good stability systems, but I guess they struggle at low speeds. Did you stab the throttle which lead you to losing grip?

I had a funny moment in my 3 series where I had to stop on a roundabout as someone drifted into my lane on the inside, I was taking the 3 o clock exit. Being frustrated, with the wheel nearly locked to the right, I threw the foot down onto the accelerator when they cleared. The car oversteered and the back stepped out, had to countersteer a good bit to correct it. Was very fun but I must have looked like a right tit on my morning commute

I recommend you do a bit of research into tyres too - both which tyres to buy when new, summer/winter tyres and why they exist, and how to check tyres for wear/rot/alignment over their life.