The radicals on WK are not the kangxi radicals that you might have heard of before, which are taught to Japanese students and are used for cataloging kanji in kanji dictionaries.
Here, the radicals are better thought of as kanji parts, which you will learn as a way of creating English mnemonics for remembering how to put together kanji that are made up of them.
When you have reached the guru level with the 川 radical, you will unlock the 川 kanji. That lesson will teach you one reading for the kanji and its meaning (which in this case you already know because it just happens to be the same as the individual radical, but that’s not always the case).
When you get the kanji to guru, you’ll unlock the 川 vocabulary word, and other words that use that kanji in compounds related to rivers.
That radical also will come back, when you start to use it to put together other kanji that contain it, like 州, 順, or 荒 (notice the different ways it can fit into other kanji).