The S2 tags area automatically imported; you should just be able to use:See the S2 FreeMarker docs for more info.
Note that there are some caveats when using the FM tags. FM tags are defined to be block or inline, and cannot be both (at least at this point, as far as I know). Some tags, like the "action" tag, are defined as an inline tag, disallowing the use of nested tags (like the "param" tag). For the most part this isn't an issue, but can be troublesome at times.