Incorrect. It's not set in the same timeline as the first game. It's a different world and universe. So you don't have to play the first game. But there might be some small details that relate to the first. But the whole game is its own thing entirely.
Understand what? Gameplay? story? There is a help thread here for anyone who needs help with the game. Some don't like it and some will, is all up to the individual. I do admit there some very oddball decisions that make it seem faulty but at best, it has a story I like a lot with characters I also like and trying to follow along is easier than most JRPG do come up with. A tutorial is in the game and there is hints you can aquire if you need extra tips on how to play effectively. Future updates not dlc related will be made to improve the game and if you want the full experience, the Expansion pass is $30 and the additional content will be sometime released within 6 months.
You can visit nintendo's youtube channel for videos about the game, they had a whole nintendo direct about it and should help you decide.
Xenoblade Chronicles 2 is a Action Adventure RPG. Battles are not turn based. Battles are done in a realtime system. Enemies walk around field, player choose if they wish to engage or disengage after encounters, or just ignore completely. Your party auto attacks within range of the enemy, while the player may use arts (special attacks) to deal extra damage and cause various status effects to debuff enemies or buff parties.