Most blog themes use a wide featured image, often 1200 × 628 or 16:9, because that is what shows on the blog and in link previews. On Pinterest a wide image appears small and gets lost next to tall pins. Bloggers who already have a good featured image for every post can reuse it as a 2:3 pin instead of designing from scratch.
Upload the featured image, type the post title and pick one of three layouts: the image on top with a title band, a stacked layout that adds a second close crop, or the full image on a blurred version of itself. The pin is drawn at 1000 × 1500 in your browser and the image never leaves your device. Have a spreadsheet of posts? Bulk mode makes one pin per row.
Which layout to choose
Title band keeps the image large at the top and puts the title on a solid band below, which is the easiest to read. Stacked shows the whole wide image, the title in the middle and a closer crop at the bottom, so it works when the image has a clear subject. Blurred extend keeps the full image uncropped on a soft blurred background, with the title above it.
All three keep the title on a plain or darkened area rather than on top of busy detail, so it stays readable at the small size pins are seen in the feed.
Reusing featured images well
A featured image chosen for your blog is already on topic, so the main change is the text. Write the pin title for search: the words someone would type to find the post. It does not have to match the blog headline exactly.
For several designs per post, try the blog post to pin set. To export the same image for every network at once, use the social size pack.