mr sourav

You can do many things after Mechanical Engineering and there are many options. What matters is your interest. I'll try to list out few of the options. 

1. If you're interested in core field, then try to look for a job. If it is difficult and you can afford it (time and financially),. If you get a good rank in GATE, you may directly land in a job in a PSU. You know right that many PSU's offer job based on GATE score? . If not, you can develop a career as Teaching Faculty in B.Tech colleges and may be go for a Ph.D.
2. If you want a reputed government job in your core field, respect in society, wanna make you family proud of you, then aim for IES and go for it. This will help you with other exams like ISRO, DRDO, BARC, SAIL, HAL etc too.