A: A concurrency, means how many tests you can run at the same time.

So if you got 2 QA testers, writing test scripts and running them 1 at a time, they would need 2 concurrency shared between them. If you schedule for various tests to run at midnight, 2 concurrent tests would run at a time.

A common pattern would be schedule most of the test overnight, with the testers, editing and checking the results in the morning. In this setup, even 2 concurrency is sufficient for covering a 100 test cases of 10 minute length each, in about 8.4 hours overnight.

I would strongly recommend giving the free public version a try (no signup required) here : https://snippet.uilicious.com/test/public/5994LUfLZKidFGJGiTxUyG

This gives you a clearer idea on what a test case for a single page would look like