TL;DR : Guild Wars 2 isn't pay to win but pay to look pretty.
You can indeed use real money to get in game gold, however the gear you can aquire with this gold has the same stats than lower priced gear with the same rarity. This come from the fact that stats on gear don't have random values but fixed values. Which means you can buy an exotic weapon for 1 gold that would have the exact same stats as another exotic that cost 300 gold. The difference in price come from the skin an equipement has. Some skins are more rare/desirable thus more expensive.
Exception made of legendary weapons which have slightly better stats than exotic weapons. However,not everyone has a legendary weapon and you shouldn't be concerned about those for a long time.
There is an in game store that provide a lot of cosmetic items and quality of life improvement (more space in inventory, more character's slots, easy travel accross the map, etc.) but nothing gamebreaking and allowing to get an advantage over other players. The money you put into Guild Wars 2 will be before anything for Character's customisation.