I've installed it already. but when I run steam it shows:
You are missing the following 32-bit libraries, and Steam may not run: libGL.so.1 Fatal Error:Failed to load steamui.so
My Ubuntu version is 10.04 LTS.
Ubuntu 10.04 is not officially supported by Valve.
It is not advised that you run Steam on your version of Ubuntu, however if you want to try it anyways the solution to your problem might be installing 32-bit compatibility libraries.
You should also make sure you have either ATI or NVIDIA proprietary drivers installed
Even if this gets Steam to work prepare to run into errors because of graphics driver incompatibility and other problems.
Please don't file bug reports on any problems occuring while using Steam with Ubuntu 10.04 because as stated by 'NikTh' it'll reach its 'End Of Life' with the release of Ubuntu 13.04 in April this year.