It will probably help if you think of a frustum (only 1 ''r'' as a set of 6 planes (Left, Right, Top, Bottom, Front, Back). Each plane consists of a normal and an offset (distance along the normal where the plane is located).

Also, you need to decide on which axis your frustum will lie/point down. I use a Z up, Y forward / into the screen, X to the right coordinate system. So my near/far planes will be located along the Y axis:

planes[NEAR_PLANE].set(0.0f, 1.0f, 0.0f, nearDistance);
planes[FAR_PLANE].set(0.0f, -1.0f, 0.0f, farDistance);

Also note that the normals to my 6 planes point towards the ''inside'' of the frustum. So the far plane points down -Y and is moved back an amount specified by farDistance.

The 4 other planes are basically just normals from the origin (offset == 0). They can be found using the horizFOV and vertFOV parameters. Get some paper and draw a few triangles that represent your FOV when looking from either the top (for left/right planes) or side (top/bottom planes). Use the hFOV and vFOV values, and then using some trig (sin & cos of the hFOV/vFOV), you can calc the normals you need.

Here''s how I calc the left/right planes... The top/bottom are similar.

  float hAng = (hFOV * 0.5f);  float vAng = (vFOV * 0.5f);  float s, c;  mSinCos(hAng, s, c); // s = sin(hAng), c = cos(hAng)      // LEFT_PLANE  planes[LEFT_PLANE].set(c, s, 0, 0);  // RIGHT_PLANE  planes[RIGHT_PLANE].set(-c, s, 0, 0);

(remember that for me, +Y is ''forward'')..

To transform this frustum to match the location of the camera, you just need to transform each of the 6 planes which it fairly straightfoward..