Kudos on experimenting with manual mode. They look fairly decent as far as camera settings go. I'm just gonna touch on the settings and not composition. On the first pic, since you're already going for silhouetted trees, next time try going even darker by increasing the shutter speed or closing the aperture a bit more. It'll make the blue of the sky and the orange bouncing off the clouds more vibrant. The longer you expose, the closer to white you get. The second pic isn't bad, but it's looking a little noisy and has a little motion blur. I'd suggest using a tripod next time to deal with the motion blur. That way you can drop the ISO way down to 100 or so to get rid of the noise, close the aperture more to increase the depth of field and slow the shutter down for a longer exposure to compensate. That'll give you a sharp, well exposed night pic. Although, the smoke rising will most likely end up with some motion blur. As far where to set everything, just experiment adjusting one thing at a time. The second flower pic is a little underexposed and the focus is a off a bit and the third flower pic is overexposed a bit. It looks like you set your exposure more for the leaves in the third one than the bee/flower. That's something to watch out for, making sure you're exposing for your subject. Experiment with taking several photos of the same scene and, in each photo, focus on a different object/area, adjusting your exposure for just that part.
I hope this helps. Just keep experimenting, it's the best way to learn.