what are the prerequisites to learn ros and make the application on ros

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That´s a pretty broad question. A good idea for beginners certainly is to use one of the Ubuntu version stated on the Installation page and follow the install instructions there. Depending on what you know better, it then would make sense to either start with the Python or C++ tutorials. It generally helps to have some basic knowledge about Linux and programming. The speed of learning will depend on previous knowledge, but following the tutorials and trying out things yourself generally will allow you to make progress best.