You do not need to know anything about the original 1995 movie to understand the 2017 movie.
The 2017 Jumanji has almost nothing to do with the original 1995 Jumanji. It is in essence a complete reboot of the franchise. There are a couple very brief references to the original, but they do not actually impact the story in any meaningful way.
The references of the original for a complete picture:
Reference #1:
Jumanji was originally a board game which brought the world of Jumanji in to our world. You briefly get an image of the original board game in the 2017 remake.
Reference #2 (small spoiler for the first half of 1995 Jumanji):
There is a brief mention of Alan Parrish. He was one of the main protagonists in the 1995 Jumanji, and played by Robin Williams. In the original movie, he is sucked in to the board game as a child and forced to survive in Jumanji for many years. He is eventually rescued and forced to complete the game as an adult.