Alpine diagram fonts: https://www.partae.com/fonts/. Using a diagram font is relatively easy. But composing diagrams with KingsRow may be easier. Modifying template diagrams is a good idea for several of the methods that I mention below.
Some people compose their diagrams for free at http://fmjd.org/dias2/index.php?game=64. This makes composing easy.
Also, if you compose diagrams as an image (GIF should be fine), in some way, you can compose a template diagram (with pieces and kings) and edit a copy of the template using any paint program. It's a quick way to compose nice diagrams, especially for use in emails. After one or two diagrams, this process gets tedious and error-prone. So this can give you headaches.
If you see a diagram style that you like, on the Internet, then you can do a screen-capture, and you can use that as a template for your paint program. You can do something similar with KingsRow. Compose the diagram on KingsRow, then screen-capture (Print Screen key in Windows), then use the paint program to reduce to a handier size. Convert to grayscale (and maybe increase contrast somehow) if your diagram will be printed in black and white on paper. You can churn out diagrams pretty fast with this method, especially if you have the runup to the position in your text or computer.
I use my word processing program to draw a border around the diagram. That's much easier than typing or drawing borders. Or your template may already have a border.
Paul Braithwaite composes nice diagrams for the English Draughts Association Journal. He uses Word tables (one cell per square). I am not sure if he fills the squares with checker characters or images. He probably uses Word to draw the border around the table.
Finally, FEN is a good alternative to an actual diagram. For example, this is the first position in B. Boland's Familiar Themes:
[FEN "W:W32,15,14:B12,7,6."]
The first W inside the quotes is whose move it is, W or B, then White's pieces, with a K in front of EACH king, then Black's pieces. You can switch White's pieces with Black's pieces. And the square can be in any order. I use FENs within PDN files in these pages.
Also see viewtopic.php?p=32063#p32063.
I would like to remind you that composing diagrams with a paint program is tedious. But changing the size or contrast or color (converting color to grayscale) of an existing diagram is easy. Different kinds of diagrams can be nicely scaled larger or smaller and retain high detail when printed on inkjet or laser printers. So don't be fooled by the lack of detail on your computer screen.
PDF (Adobe Reader, which is a free program) files can have diagrams made from fonts or images. Your word processor probably has an option for including the font as part of the PDF file. Images are included in PDF files automatically.