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How to start contributing?

I am Ashutosh Yadav currently studying in indian institute of information technology
vadodara, India in Information technology.

My fields of interest are datastructures and algorithms as i was doing competitive programming for a while . I want to start contributing to the open source project .But i have no idea how to start ,it totally confusing. Can you help me out .I know java, python ,c,c++,html and css.