I had this issue when I was a beginner.
Weak muscles can shake or "shiver".. really it just takes time to get past it
A lot of it could be your stabilizer muscles such as biceps and core during a bench press aren't quite up to par yet, but balancing the bar during a bench press is a workout in itself. I had this issue until I surpassed 100 lbs on the bench press. You can also expedite it sometimes by using dumbbells as it forces you to find balance right away.
As long as you are using correct form, this is fine.. although it might help to prevent injury if you start a linear periodization program with blocks which is great for newbies and also builds up those muscles. Really I think what's best is to do a few months of dumbbell or unilateral training and try to keep reps above 8. This is just based off my beginner experience however. This will prevent asymmetrical muscles which is really common starting out, and fix those balance issues or the weak shivering muscles at least. Just give it time