About software installation!!

Two users are going to intall the same software in their separatte system, will there be some mistakes arise?
  When I'd like to install a software as a common user, not the root, it said" permission denies". So, I want to ask: if I want to install a software in my system, do I have to do it as a administrator? As a common user, am I able to intall a software?
   Thank you!

有些可以有般用户，有的定要用root.因为要向一些系统目录向文件。