You have made an important observation in optics, which is the science of light, and an important field of physics.
Light can travel through transparent (see-through) materials like glass, plastic or water, but it does not pass through them unchanged. The transparent material has a different density than the air it is traveling in, causing the light to change direction inside of it. This is called refraction: its why observations made through water are distorted or offset and it is also how lenses work.
In a lens, light is refracted different ways depending on the curvature of the surface and the material's properties. Under the right conditions, these materials can bend light rays to make things look bigger than they are (they can magnify). Many optical devices (binoculars, eye glasses, telescopes, and microscopes) use the same basic ideas of bending light to fool your eye and brain so it appears to come from larger or closer objects. The magnification depends on the distances between the lens and the image and the lens and the object.
A convex lens curves outward in the middle and can focus light rays to magnify an object. Water in a curved container or water droplets (both highly curved and convex) can thus be great magnifiers.
This is in contrast to a concave lens, which curves inward in the middle and spreads light rays out. Looking through this kind of lens can help us focus our eyes on something far away.