A synthetic language is like a puzzle with little pieces called "morphemes" that fit together to make words. Just like we can put together letters to make a word, in a synthetic language we use these little morphemes to create words.
For example, let's say we have a morpheme called "cat" and another called "s." We can put them together to make the word "cats." A synthetic language often has many different kinds of morphemes that can be put together in different ways to create new words.
Another thing that's special about a synthetic language is that each of these little morphemes can tell us something about the meaning or grammar of the word. For example, in some languages, adding a special morpheme at the end of a verb can tell us if the action was done in the past, present, or future. So, just by looking at the way a word is put together, we can learn a lot about what it means and how it fits into a sentence.
Some examples of synthetic languages include Latin, Russian, and Hindi. These languages can be a bit tricky to learn, but they can also be really fun because they're like a big puzzle waiting to be solved!