i am using optical flow to track some features i am a begineer and was tol to follow these steps

Match good features to track 
Doing Lucas-Kanade Algorithm on them
Find homography between 1-st frame and current frame
Do camera calibration
Decompose homography map

Now what i don't understand is the homography part because you find the features and track them using Lucas-Kanade, now the homography is used to compute camera motion(rotation and translation—between two images). but isn't that what the Lucas-Kanade does? or the Lucas-Kanade just tracks them and the homography makes the calculations? I am struggling to understand the difference between them, Thanks in advance.
Optical flow: detect motions from one frame to the next. This is either sparse (few positions of interest are tracked, such as in the LKDemo.cpp example) or dense (one motion per position for many positions(e.g. all pixels) such as Farneback demos in openCV).
Regardless of whether you have dense or sparse flow, there are different kinds of transforms that optical flow methods may try to estimate. The most common transform is translation. This is just the offset of postion from frame-to-frame. This can be visualized as vectors per frame, or as color when the flow is dense and high resolution.
One is not limited to only estimating translation per position. You can also estimate rotation for example (how a point is rotating, from frame to frame), or how it is skewed. In affine optical flow, you estimate a full affine transform per position (change translation, rotation, skew and scale). Affine flow is a classical and powerful technique that is much misunderstood, and probably used far less then it should.
Affine transforms are given most economically by a 2x3 matrix: 6 degrees of freedom, compared to the regular 2 d.o.f. of regular translational optical flow.
Leaving the topic of optical flow, An even more general family of transforms is called "Homographies" or "projective transforms". They require a 3x3 transform, and have 8 d.o.f. The affine family is not enough to describe the sort of deformation a plane undergoes, when you view it with projective distortion. 
Homographies are commonly estimated from many matched points between frames. In that sense, it uses the output of regular translational optical flow(but where the affine approach is often used under the hood to improve the results).
All of this only scratches the surface...
Homography and Lucas Kanade what is the difference?