How to add a drop cap to a paragraph
Add a drop cap in Publish by Zaweba with Format > Drop cap, choosing 2, 3 or 4 lines; the large letter lines up with the text beside it.

Put your cursor in the paragraph, then choose Format > Drop cap in Publish by Zaweba and pick 2, 3 or 4 lines. The first letter grows to that many lines tall and the rest of the paragraph wraps beside it. Publish measures the letter from the font, so its top lines up with the capitals of the first line and its baseline with the last line. The app is free and works offline.
A drop cap is the big first letter you see at the start of magazine articles and old books. It tells the reader where the story begins, and it gives a page of text a bit of shape.
Choosing the size
The number of lines sets how tall the letter is. Two lines is subtle and suits narrow columns, where a bigger letter would push the text too far across. Three lines is the classic magazine size and works for most newsletters. Four lines is dramatic, good for a feature article or the opening page of a booklet, but it needs a reasonably wide column to look right.
Try each one and look at the whole page rather than just the paragraph. The right size is the one that catches the eye without shouting over the headline.
Why the alignment looks right
Many programs just make the first letter bigger, and it ends up floating slightly high or sitting a little low. Publish measures the drop cap from the font itself. The top of the big letter lines up with the top of the capitals in the first line, and its baseline sits on the baseline of the last line it spans. That's what typesetters aim for, and it's why the result looks deliberate rather than approximate.
Because the measurement comes from the font, it's worth glancing at the drop cap again after you change the body font, just to enjoy how the new letter shape sits.
Using drop caps well
Use them sparingly. One drop cap at the start of each main article is plenty. Put one on every paragraph and they stop meaning anything.
Start with a letter that has a clear shape. Most letters work well, but a paragraph starting with a quotation mark or a number can look odd. Rewording the first sentence slightly often fixes it.
Pair it with the first few words in bold if you want a stronger opening. A character style can hold that look so every article starts the same way.
Mind the columns. In a text box with several columns, a drop cap in a narrow column eats a lot of width. Two lines is usually safer there.
Where it fits in the rest of the app
Drop caps sit happily with the rest of Publish's text tools. Linked text frames let a story flow on to another page with the drop cap still at the start. Paragraph styles keep the body text consistent. Text wrap keeps pictures from crowding the opening.
The drop cap stays real text. It exports as selectable text in PDFs and looks the same in exported pictures, because the screen, pictures and PDF all use the same font measurements.
Add one to the lead story of your next newsletter and see how much more finished the front page looks.