Where should i put dll file(that i use in my project)

I presume you are asking about third party dll files, because the output (exe/dll) files generated by the project are better left unmanaged by SVN, because they are regenerated on each and every build.

What I usualy do is create a Lib folder, that is on the top level of my source tree, and put all needed references there, usually in additional folder divided by tool or by functionality (logging, emailing, apis, etc, etc...)