user10190: I started a game (with the black pieces) where I have the possibilty to play the Grünfeld that I never played before.

1.d4 Nf6 2.c4 g6 3.Nc3 d5

I want to know what's the main idea behind it, especially for black, since I heard that it could lead to sharp positions and complications (even Kasparov had a hard time playing it against Karpov)  

user7297: The main idea behind the Grünfeld is that Black momentarily concedes the center to White, only to attack it later.
For example, in the Exchange variation, White often gets a pawn center (c3, d4, e4) while Black will put it under pressure (especially aimed at the white d-pawn). Below is a diagram with a typical pawn structure for this variation, and some black pieces on squares where they can often be found.
[FEN "3r2k1/pp2ppbp/2n3p1/q1p5/3PP3/2P5/P4PPP/4K3 w - - 0 1"]


10190: <p>I started a game (with the black pieces) where I have the possibilty to play the Grünfeld that I never played before.</p>

<blockquote>
  <p>1.d4 Nf6 2.c4 g6 3.Nc3 <strong>d5</strong></p>
</blockquote>

<p>I want to know what's the main idea behind it, especially for black, since I heard that it could lead to sharp positions and complications (even Kasparov had a hard time playing it against Karpov)  </p>
 7297: <p>The main idea behind the Grünfeld is that Black momentarily concedes the center to White, only to attack it later.</p>

<p>For example, in the <a href="https://en.wikipedia.org/wiki/Gr%C3%BCnfeld_Defence#Exchange_Variation:_4.cxd5_Nxd5_5.e4" rel="nofollow">Exchange variation</a>, White often gets a pawn center (c3, d4, e4) while Black will put it under pressure (especially aimed at the white d-pawn). Below is a diagram with a typical pawn structure for this variation, and some black pieces on squares where they can often be found.</p>

<pre><code>[FEN "3r2k1/pp2ppbp/2n3p1/q1p5/3PP3/2P5/P4PPP/4K3 w - - 0 1"]
</code></pre>
