There's a "finger" that holds the bobbin case in place. It's usually to the back, left of the bobbin case. The metal is pretty soft. So you can usually press it back in position with your own finger. The thread passage in the front, right of the bobbin area has a small spring that the thread passes through. When that gets noisy, there's usually a burr on the plastic bobbin case. Sometimes we can polish it smooth with a very fine sandpaper (about 400 to 600 grit).
If you want an inexpensive machine that will sew layers without a problem, get a vintage Kenmore. The best ones have a front-loading bobbin (not drop-in), low-shank presser foot (not super-high shank as these sometimes have left-homing needles), and built in stitches (not cams).