Hey Xiumei Shi, thank you for sharing your questions in the Community!

You can use shift + return on a Mac to create a line break in a table cell (or outside of a table) in our editor. 

This video includes another work around as well:

You can create line breaks outside of the table then copy + paste them into the cell as is.

Also, as your list gets longer, remember you can adjust the size of column in a table by clicking + dragging the right edge of the column. I hope this is helpful! Happy to chat more if you have any other questions.