seeing blunders when opponent has no loose pieces

Turns out there isn't much out there for people that are below 1000 rating. However, this crash course I am about to link to you is geared towards players like yourself who want to learn the basics of the game. Just go to this site and enroll in the beginner's crash course, which is for free.
https://www.chessvl.com/courses

Facepalm!
I don't know if I have the fortitude and patience to teach a rank beginner. Lol
You need to play MUCH slower chess. Your not looking more than .5 to 1 ply ahead, and often zero ply ahead.
I would recommend doing lot's of mate-in-one problems, if only so you get used to looking at the board. If possible, do single move tactical problems. Problems like looking for pieces that are "en prise", or sitting out just waiting to be taken.
Even grandmasters come across en prise pieces, although usually after they do a lot of ground work to strip it of all it's protectors.
I lost a game earlier today like that, but my opponent worked his butt off to get it. It took most of the game for him to hit paydirt. -I lost a bishop, FYI.