this message:

"Catalyst System: Bank 1: Efficiency Below Threshold"

means that the reading of gas at the oxygen sensor (pre-cat) and the reading of gas at the probe (post-cat) are too close to eachother.

There is a "threshold" difference between the two, and if the values fall below that difference (i.e. get closer together), it usually means the catalytic converter is not doing its job, which usually means it needs to be replaced.

The misfire one should be self-explanatory. Finding the cause, however, might be a bit tough.