When you select your title or paragraphe text block, you'll have the following menu appearing on your right side.
As you can see, you can easily make your text bold, italic, underline, strikethrough and uppercase or lowercase your letters.
You can also use the keyboard shortcuts to access the bold, italic and underline with:
Bold: Cmd + B or Ctrl + B
Italic: Cmd + I or Ctrl + I
Underline: Cmd + U ir Ctrl + U