Have you tried to follow the docs?
It includes an example of how you would use it in markdown:
[Text](https://www.gohugo.io "Title")
And the render-link code that you put into layouts/_default/_markup/render-link.html
:
<a href="{{ .Destination | safeURL }}"{{ with .Title}} title="{{ . }}"{{ end }}{{ if strings.HasPrefix .Destination "http" }} target="_blank" rel="noopener"{{ end }}>{{ .Text | safeHTML }}</a>