The SCM homepage contains links to precompiled binaries and source distributions.
Downloads and instructions for installing the precompiled binaries are at http://people.csail.mit.edu/jaffer/SCM#QuickStart.
If there is no precompiled binary for your platform, you may be able to build from the source distribution. The rest of these instructions deal with building and installing SCM and SLIB from sources.
Download (both SCM and SLIB of) either the last release or current development snapshot from http://people.csail.mit.edu/jaffer/SCM#BuildFromSource.
Unzip both the SCM and SLIB zips. For example, if you are working in /usr/local/src/, this will create directories /usr/local/src/scm/ and /usr/local/src/slib/.