First you need a business plan.
Operating a resturant requires an investment of dozens or hundreds of thousands of dollars, and is an excellent way to work 18 hours a day for about $1.00 per hour net return.
Depending on the type of restaurant, you may need an ordering system specific to the restaurant industry, like the Squirrel systems you see with touch screens for the wait-staff. If it's a pizza delivery place you're looking at obviously the needs will be different.
You will want an accounting program, which may be intgrated with the restaurant program (above). Usually, you buy integrated restaurant management programs, you don't roll your own in Filemaker or something. And you usually dont get these on Macs.
You'll want to be able to prepare menus and printed materials fairly easily, and cost out your ingredients and menu items.
But don't put the cart before the horde here: your first job is to accurately assess your market area, competition, potential customers, their food preferences and your costs (both fixed and operating) and build a cash flow model. Health code compliance, taxes, insurance (esp. if you are serving liquor) wasteage and theft, and hiring/managing staff are also biggies.
Smart restaurant owners can make money - although these are usually families where everyone works their butt off for years at no pay until they are established. Something like 80% of restaurant owners lose money though.