Two ways:
1. If you are using a text frame, reduce its width so the letters arrange themselves vertically. Make the text centre-aligned. This may not work if the text contains wide characters such as w's, unless you are using a fixed width font like Courier New.
2. When typing the characters add a line break after each one. Shift+Enter adds a line break. This works in both frame and artistic text. Again, use centre-alignment for the text.
You could, of course, use method 1 initially, the use method 2 only where necessary if two letters appear side-by-side.
There is no option for "Vertical Words", but Line Spacing can be done from both the Paragraph and the Character tabs, or in Format/Paragraph dialogue.
Credendi non mutant facta