i. Students
ii. Teachers
iii. Sentence Contributors
iv. Textbook Publishers
Specify to the website what textbook you're learning from, what chapter you're in, and ask for sample sentences to read.
Add some sample sentences and specify that they can be understood if the student has read to a certain chapter in a certain textbook.
Assemble a collection of sample sentences for your course from existing sentences on the website.
Contribute translations of existing sentences.