Are you asking about the engine oil or transmission fluid? Engine oil is 3000-6000 depending on how you use your vehicle and the manufacturers recommendations. Consult your owners manual regarding transmission fluid.
Manual transmission oil change intervals vary from vehicle and manufacturer. Most recommend between 30000 & 50000 miles, and then again every time you add on that mileage. Check your owners manual or call the car dealer who handles your brand. They can give you the exact data.
It really depends on how you drive and where, if you really want to know here's how to find out. At around 3-4000 miles start checking your oil, not a lot, once a month maybe, just till you know. You'll see when the oil starts to look and feel dirty. About the 3000 mile oil change, the auto people I've talked to say the advertising campaign worked, that's where that came from, cars don't need an oil changes that soon. Who knows.