What can I do to get information about my father's death? Meaning his assets, his house and if he left a will or not?

Okay, so my Father passed away in 2004 when I was a young boy, and he was doing good he had his own house was in the lathering industry. I was a young boy so I didnt really know the right questions to ask or didnt pay attention to things I wish I would of been older to answer for myself or not. But now that I'm an adult I want to find out everything that happened after he died. Because his girlfriend he lived with and had a kid with which is my half brother that I haven't gotten to see since my dad passed away. But I believe she took everything he owned from me so I couldn't have one thing. I was a kid so I didnt know how to really feel. I grew up with my mom and she didnt talk about him or tell me anything at all. Still hasn't. I'm 21 years old and dont know what rights I have/had towards his belongings & if he had life insurance or like his house ? I need the right direction so I can finally find the answers I deserve and finally rest my mind. He died in Idaho falls in 2004.