Just been playing with cacti on my webserver, but the graphs dont seem that easy to understand?

Could someone shed some light on these results>??

Memory Free::

Current: 97mb
Average: 77mb
Maximum: 101mb

Memory Buffers::

Current: 67mb
Average: 68mb
Maximum: 68mb

Cache Memory::

Current: 3.7Gb
Average: 3.8Gb
Maximum: 3.83Gb

Good, bad or ugly?