For personality or scored quizzes
While editing a question, click "answer settings" just above your answer choices
Now you'll be able to enable "Select Multiple Answers" for this question. Then you'll be able to set the minimum amount of answers someone has to choose as well as the maximum. You can leave the minimum at "0" if you don't need people to select more than one answer.
Once you select "Select Multiple Answers" a "Next" button will come up at the bottom of the question because now you need people to click "Next" once the've made all the selections they want on the question. There are some customizations to the design of this button you can make.
The first is position, you can choose to have this button hover over the answers choices and be "fixed" at the bottom of the screen. The reason you'd want to do this is because a question with lot of answers might fill up more than the whole screen, especially on phones or other mobile devices, so you want the "Next" button to stay on the screen.
The difference with assessments is that you have to indicate which answer choices are correct.
So if I have a question like the one below, "Which countries have won the world cup?" then I can click "Answer Settings" and check the box for "Select Multiple Correct Answers"
Then you need to click "Set Correct Answers" on the right and choose all that are correct.