I am a co-author in a paper. How can attending a conference be beneficial to career and resume since I am not sure whether to attend it.
Unless you are presenting a paper at a conference, there isn't much advantage for your résumé. From a professional and educational perspective, however, conferences can be very informative, for the reasons Peter outlines.
I would go a little bit further than Peter, however, and recommend that, if possible, you try to attend multiple conferences per year, particularly if you are relatively early on in your career. At least one should be a relatively large meeting, where you can make many contacts in your general field; and one, if possible, should be a smaller meeting or workshop, where you can interact with your peers in your specific field. That way, you get the benefits of learning about the overall field—which is important for networking and job-finding, as well as the close-up exposure to work related to your own.
Since conferences are the places where new science results are typically first presented, going to conerences can be very rewarding. You will most likely get an overview of the area within which the conference lies. You will meet and hear many researchers you may only have heard about or read. You also have the opportunity to network and find others that are working on similar or related topics. So there are several reasons for going and if you intend to stay in academia you should make it a habit to attend at least one per year (depending on costs and travel etc.)
Conferences provide opportunities to learn about the latest research in your field. Additionally, conferences also help in networking. Networking often increases your chances of collaboration in future projects. You should attend as many conferences as possible as this will make you a known figure in academic circles. It will also be beneficial for your CV as it will create the impression that you are an active member of the academic community.