Creating a LUT
Creating a new Identity LUT is super easy with Lattice. You can use ⌘N, File->New LUT, or the "New LUT" button on the bottom left corner of the "Welcome to Lattice" window. Once you've arrived at the New LUT window, you'll be presented with several options for setting up the LUT.
Lattice can create 1D and 3D LUTs. If you don't know what kind of LUT you need to make, you can learn more about them.
The default sizes (33 for 3D, 4096 for 1D) are generally good for most use cases. If you have to make a particularly complex 3D LUT like an ACES pipeline or a transformation from a very wide gamut to small gamut (like DCI-XYZ to Rec709/Gamma 2.4), you might want to use a larger size, like 64. If you're making a 1D LUT that transforms from floating-point scene linear into camera log or a display-referred space, you will probably want to use a size 65536 (16-bit precision) LUT.
The Input Bounds describe the range of values that the LUT can affect. Unless you're making a LUT that needs to transform scene linear values (high dynamic range values greater than 1.0) or another special case, you'll want to leave the minimum at 0 and the maximum at 1.