If in the past getting it installed on CentOS6 meant jumping through hoops with the latest major version of CentOS those issues have been overcome thanks to updated system libraries and the availability of repositories such as Nux Dextop that package Steam into a nice and friendly rpm.
Basically to have Steam working on CentOS7 you'll need to execute a few steps:
1) Enable Nux Dextop and EPEL repositories
2) Install Steam
3) Launch it
4) Have fun
In other words:
# rpm -Uvh http://ftp.up.pt/fedora-epel/7/x86_64/e/epel-release-7-5.noarch.rpm && rpm -Uvh http://li.nux.ro/download/nux/dextop/el7/x86_64/nux-dextop-release-0-5.el7.nux.noarch.rpm
# yum install steam libgudev1.i686
As for step 4, I suggest installing Team Fortress 2 :)
Now launch Steam, go through the graphical install and provide your account credentials to login.
As an off-topic side note, consider having a YUM plugin to manage repositories so that base CentOS packages aren't replaced by those from third-party repositories, personally I use protectbase.