You can enter any text that you would like in the form at the left -- for example, a paper that you've written, or a newspaper article that you've copied from another website. After inputting the text, you can then see useful information about words and phrases in that text, based on data from the Corpus of Contemporary American English (COCA).
First, it will highlight all of the medium and
lower-frequency words in your text and create lists of these words
that you can use offline. This frequency data can help
language learners focus on new words, and it can allow you to see
"what the text is about" (i.e. text-specific words). You can also
have it show you the "academic" words in your text.
Finally, you can do powerful searches on selected phrases in your text, to show related phrases in COCA. In this way, this resource is like a "collocational thesaurus" to see what related phrases are most likely in different styles of English. For example, if you click on the words potent argument in the text that you enter, it will suggest alternate ways to express this (e.g. powerful or convincing argument), and it will show you the frequency of those phrases in COCA -- overall, and by genre. This will help you use "just the right phrase", based on a huge collection of native English texts.