Students can click the hand button at the top of their screen to indicate to their teacher that they need help.
From Current Status, you will see a "1" with a hand symbol pop up under the Help Order column. The "x" will clear the help for that student - you should click this after you've helped that student. Additional students asking for help will be listed in order in this column.
Clicking on the student's name (shown above) will show you the current problem they are working on, as well as the correct answer (shown below).