Line break in tables

Sorry if I seem thick, but - I was trying to insert a line break in a table.
I have tried

• inserting a line break
• inserting two spaces where I wanted the break
• inserting <br> and <br />
  The first splits up the table, the second is shorted to one and the latter is simply inserted as text.
  I am assuming I am missing something?

The following worked for me:

| Col1 | Col2 |
| ---- | ---- |
| a<br>b | a b |