wait checks every 0.1s for the block to return true or "anything but false" until max_seconds has elapsed. Quits the script with an error if the wait condition is not satisfied.

wait max_seconds do
  # true or anything but false
end

Wait maximum of 3 seconds for the text 'Example Domain' to appear on the page.

visit 'example.com'

wait 3 do
  has_text? 'Example Domain'
end

Wait up to 3.3 seconds for a <div id='login'> to appear and assign it to a variable for clicking.

login = wait 3.3 do
  find 'div#login'
end

login.click