So what your being asked is, "This animal has short legs and its hut is large. Lives near the rivers and bathes in the river." I'm thinking that the animal is probably a Hippo because they have short legs and live under water, but turtles have a large hut(their shell on their back) as well as short legs and live in the water. I'm kind of leaning more towards a turtle being your answer. So what you would write in Spanish is "Tortuga" which means turtle/tortoise. Hope this helps!
Try listening to music such as songs by Selena and try to pick out the words that you know. If you watch a show that has Spanish in it, listen for words you know and see if you can figure out what they are saying. You can also try asking friends or family to quiz you on words or have them ask you what certain words mean in Spanish. Write down as many words you can remember in Spanish and look up new words you want to learn to grow your vocabulary.