Look in the article section and at the stickys in the marine sections.
Here's a run through of what I would suggest you use for your setup, prices are only approximate, the costs will depend on where you live and where you buy your stuff:
55g tank: $40-150
4ft shop light: $30
10k and actinic bulbs: $40-60
Coralife super skimmer, 125g model: $200-300
4x Maxi-jet 1200 power heads: $80-120
Heater: $30-50
Substrate (sand or nothing at all): $0-60
Live rock, 20-30 ilbs: $100-450
Base rock, 20-30 ilbs: $ 40-80
deionization unit: $40-100
Total: $600-1,1350
On top of that you will need your salt, stand, a way to suspend the light above your tank (could be hung from the ceiling, mounted in a canopy or rested on blocks of wood) and you also need a quarantine tank (10g with power filter and PVC piping for decorations). If you get a disease in the main tank, there is almost no way to effectively treat it without making your tank a death trap for any kind of invert life (corals, crabs, snails, shrimp, etc.), so you do need a quarantine tank.
Down the line, if you want to start keeping corals, either add a second shop light, or switch the existing fixture to very high output (which means getting new bulbs and a new ballast).
