A corpus has to be selected before you can start using any of the Sketch Engine features. If you are a new user, it might not be clear which corpus you should be using. Here are a few tips for beginner users.
Featured corpora are a good start for monolingual corpora. These have been pre-selected based on the size and the availability of maximum number of features.
No featured corpus?
If there is no featured corpus in your language, switch to All and use the drop-down to select the language and pick the largest corpus.