Rotini is a corkscrew shaped pasta made from semolina flour. The grooves in the pasta helps the pasta sauce to adhere well. The spiral pasta is typically about 1 to 2" long. These are really just larger size fusilli and in fact this pasta is not called rotini in Italy. In addition to typical white pasta rotini come tri colore (tri - colored) flavored with beet, spinach and tomato.
This is a perfect pasta to use with thick tomato sauces, for pasta salads, and it works well served with a classic Carbonara sauce. This is a good recipe for Rotini With Basil Sweet Peppers & Italian Sausage.
Most any well-stocked grocery store would typically carry this pretty common pasta. If they don't have it, buy fusilli which is essentially the same thing. I like to use the tri colore in my Tri Color Pasta Salad With Prosciutto and Feta one of my favorite summertime dinners.