If you want to examine a few water animals collect then in a wide mouth jar filled with water from the stream or pond where you found them. Never add tap water, the chlorine and other chemicals in the water is not good for them. Examine the creatures and sketch them in your Nature Journal, but put them back where you found them before any harm comes to them.
If you are at the beach, take along some buckets, shovels, collecting bags and your Nature Journal. A few guidebooks to seashore life is good to bring along too. Collect seashells or empty crab shells, Glue them onto cardboard to make a collage or create a hanging mobile using thread, all purpose glue and driftwood.
A good way to learn why one habitat is different from another is to study what creatures live there. How do freshwater and salt water habitats differ?