Here's a quick but informative answer.
The Witcher 3: Wild Hunt is one of the most critically acclaimed video games of all-time. People interested in playing that game are always asking:
"Should I play The Witcher and The Witcher 2: Assassins Of Kings before I play The Witcher 3: Wild Hunt?"
I recommend starting with The Witcher on easy mode (to get it over with) only if you're willing to endure its clunky combat, and poorly optimized game engine for 35-hours (the main story).
The only really good thing about the first game is its in-depth explanation of the witchers, and overall story.
If 35-hours of mediocre gameplay is turning you off, I suggest watching the following video that provides a recap of the story:
Before you play The Witcher 3, you should definitely play the solid The Witcher 2, because five decisions that you make in that game will affect the next game.