Where do I put backlinks on my website?

Generally speaking, anywhere they’re useful. You should link from your website to add to the reader’s experience; not to simply link out from your website. If you’re writing about a topic and you feel it would add to link to an article or resource that goes into more detail on a specific area, then do so. The other area here could be a resource or link page that you create to collate lots of content about one topic and put it in one place.