There's a couple of ways to do this in Blogger-land.
In a blog post, using Blogger's editor, you can use the link tool (up there next to the "add an image" button) to insert a clickable link. You just add the URL e.g.www.fredbloggs.com and a nice phrase to display that will be underlined and clickable e.g. Fred's Blog.
Alternatively, you can write the little snippet of code yourself in the editor's "edit HTML" mode. Comment boxes on Blogger also accept the little snippet of code directly and it's worth learning to use this code as there is no tool on comment boxes to add links (that I know of).
So you just need your target URL and the text you want to be able to click. The format to use is shown below (apologies, I had to put this in as an image as Blogger keeps trying to actually interpret the code instead of displaying it). The first line is just to show the syntax and the second line is an example of an actual URL.
Make sure you get the < and > parts right or Blogger whinges like mad and remember those quotes around the URL.