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The first step in programming anything is figuring out exactly what you want the program to do. Yes, you want to make a robot follow a line, but how will it do that? What kind of sensors does it have?

If you have one sensor that can detect when you are on the line and when you are off of it, the simplest (but not very efficient) method of following the line is to have the robot turn one way until the sensor leaves the line, then have it turn the other way until the sensor detects the line again. There are better ways to do this, however.

Once you figure out what you want to do, then you can start writing code.