It means you have to add that line of text to the .Renviron file, obviously replacing [your_user_id] by your actual "user ID".
Although, I don't think this is going to solve your problem, since you are missing a system library for which the corresponding R package is just a wrapper.
I think you need to contact your system administrator and ask them to install the missing system dependencies.
You are right, those steps really didn't solve my problem. But the staff said that 'As being used of the R, there might need to install and update many third-party libraries and plugins. In order to be more flexible, you are to install the libraries in our HOME directory without any further permissions required'.
The strange thing is that after logging in with his personal account, he can successfully install the two R packages 'curl' and 'xml2'. I'm new to HPC and I'm wondering, aren't our configurations the same?