Blue Bear Sound said:
A mastering house........
Blue Bear is right.
If your intentions are to produce a commercially viable CD you should have someone with a dedicated room and equipment to process the overall mix. Any form of DSP processing that you apply to the overall mix degrades the sound further by introducing quantization error and other artifacts. Additionally if you add compression you may damage the audio to the point that a mastering engineer will not be able to recover lost transients and headroom.
A mastering house will use gear that is dedicated to this process using EQs and compressors costing thousands of dollars. A plugin is simply not going to have the same quality. Also a mastering engineer will serve as an objective listener which can be extremely helpful if you're listening to your material in the the same room, same speakers, and with the same pair of ears.
That said, if you're budget-constrained and just want to fool around, the first step isn't deciding what gear to use, it's deciding what your material needs.
First complete your mixes and create a CD without any processing. Compare these CDs to a commercial CD of the same style and listen objectively. If they sound close, you're done. If not, decide what you can do to the individual elements of the mix to fix it before slapping on something on the main stereo buss.
Once you have the mix to the point where you feel that you can improve it no further, make a list of the things that bother you. Is it level? Then start working with a combination of a separate compressor and limiter. Is it frequency balance? Find out the frequencies that are innappropriate using a spectral analyser or by "sweeping" a parametric EQ and EQ them out. In some cases you may want to try a multi-band compression to raise or lower those areas, for example sibilance or a bloated bottom end.
Always keep the unprocessed version of the mix in as high quality as possible and master from this version. For example if you can bounce or render the file to 24 bit, keep it there, don't bounce to a 16 bit 44.1K until the last step and dither at this stage. Also if you decide later that you can afford to send your material to a mastering house, the engineer will have a better version to work from.
There's alot more to this, but hopefully this will get you started ...