Now im thinking about getting it. What are somethings i need in order to make it fun or is just the original good enough (to start

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The first basic game allows for hundreds of different games by selecting different card sets. Most of these different setups demand or at least favor a separate strategy, which the players need to develop on their own.
Later sets and extensions partly change the flow of the game. Not every player sees every expansion as a good contribution to the game. You best start with the first set and play some hundred games with it.
Also what are the goals of the game ...
... to score the most victory points.

VPs come as cards which you can buy like all the other cards (action cards, money). The go into your deck, where they are dead weight, though. Dominion is a balancing act where you have to find the sweet spot between buying cards for a powerful and efficient deck and buying victory points for your score.
Technically, Dominion is a deck-building game. Each player starts with the same cards, of which you draw five for your turn. With these five cards you can start actions (Play one card) and buy one new card.
It starts getting interesting when you can play card combos for great effect: Start with a Village (Draw one additional card, play two more cards), play a second Village, followed by some Mines (Upgrade one coin card to the next highest type) would be an extremely simple example.
This thing (drawing five cards, playing one and buying one) proceeds until either three stacks of cards or the stack with the most valuable VP card is depleted. Now each player counts the VPs in his complete deck.
... and how hard is it to learn and teach?
When four players withou any previous Dominion experience learn the game together, the first one or two games might be a bit bumpy because of the unusual concept. After that it plays extremeley smooth and teaching it becomes easy. Just make sure that newcomers aren't shredded to pieces in their first game.
Probably the only kind of gamers who won't like Dominion so much are those who demand heavy interactions between players during the game. This isn't one of Dominion's fortes.