what type of oil should I used and should it be regular oil?

5W-30 is a standard choice when it comes to weight. Most brands sold in parts stores, meet current oil specs for your vehicle. "Regular" oil (non-synthetic) is perfectly suited for your automobile, just make sure you change it on regular intervals, like every 3,000 miles. Some Trailblazers have an "oil life" warning, to alert you its time for service, but this usually illuminates every 5-7K miles, which is too long. Use an oil change sticker and adhere to 3K. Good luck!