Long Posts and post summaries

On other blogs, I've seen that authors will write a summary or intro to the post and then there will be a link the reader can click to go to the full length article. Given that some of my technical posts are going to be very long, I'd like to do the same thing here. But I've read some of the guides on blogger as well as other various websites about how to do that and the instructions are real head scratchers, telling me to look for tags that don't exist to insert code.

Considering the guides tend to be really old, all I can imagine is that they are out of date and that some new approach is required to accomplish what I'm looking to do. If anyone has any advice or information about implementing that feature for this blog, I'd love to hear about it.

An example of what I'm talking can be seen on this blog here:
http://afkgamer.com

If you flip through a few pages of posts, you'll find longer posts where he sets up the post, and then there's a 'Read the rest' link or whatever to follow in order to read the rest of the lengthy post.