Most of your interaction will be by typing commands into a sage cell. Just below this paragraph is an empty cell. Click once inside the compute cell and if you are in the Sage Notebook, you will get a more distinctive border around it, a blinking cursor inside, plus an “evaluate” link below.

At the cursor, type 2+2 and then click on the evaluate link. Did a 4 appear below the cell? If so, you have successfully sent a command off for Sage to evaluate and you have received back the (correct) answer.

Here is another compute cell. Try evaluating the command factorial(300) here.