This question already has an answer here:
This error could be caused by required additional software packages which are missing or not installable. Furthermore there could be a conflict between software packages which are not allowed to be installed at the same time.
The following packages have unmet dependencies:
steam-launcher: Depends: curl but it is not going to be installed Depends: libc6 (>= 2.15) but 2.15-0ubuntu10.4 is to be installed
How do I get these? because with out them I can't run Steam