"Do-follow" link is just a normal hyperlink with anchor tag. There is no step involved in creating dofollow link. Just create a normal hyperlink without nofollow tag. Here is an example;
<a href="http://techulator.com"> Techulator </a>
The other type of link is "No-follow" link. It want invented by Google to fight with link spam. Here is an example of nofollow link;
<a rel="nofollow" href="http://techulator.com"> Techulator </a>
Backlink (dofollow) is one of the most important ranking factor in crawl based search engines like Google, Bing, Yahoo! etc. However, it is the most overutilised factor by SEOs.
Here is how it works;
Consider, Blog A is tech blog. Blog B which is also tech blog gives a link to Blog A. After few days, Google bot crawls Blog B and indexes that link. Now Google will consider this link as a vote/signal to the Blog A. Hence, it will rank higher in SERPs.
Points you should consider:
1. A contextual backlink carries more weightage. For example, a link from article body is better than a backlink from comments.
2. Only dofollow backlinks are considered as ranking factor. Nofollow links aren't.
3. Try to get backlinks from a blog which is similar to the niche of your blog.
4. Don't create thousands of backlinks. Consider, quality over quantity.