I understand you! Doom can be quite intimidating for beginners compared to others shooters. I would run through Knee Deep in the Dead on lower difficulties to get an idea of how levels work. It teaches you keycards, enemy placements, secrets, basic navigation, etc. Doom is meant to be played in the way that makes you feel most comfortable and the lower skills are there for a reason. Do not feel obligated to rush into hardest difficulties because of peer pressure, because the word "doom" does not just mean one thing to every one person. :)