Can we making a social networking sites like orkut ... Is it legal? Not the exact orkut , but every social networking sites have some common features... Can we use them
Unless the feature is patented, then yes it is legal to reproduce a feature you've seen on another website. If the name of a feature is trademarked, call it something different.
If a feature is open source, you are free to use it. If a feature is unavailable, you can construct it aslong as you don't copy the source code or "reverse engineer" it. Make your own.