Now if you're programming a plugin and I'm the spigot 1.14.4 API, but the tutorial is for the 1.8. Is it possible to program after the tutorial?
So can one program with this API as with the 1.8 API?
Yes, many things are the same, but there are also some serious changes. This you have to fix then probably yourself.
Yes, the basics of the Spigot library have remained the same. If something changes you will notice it and then googling as it is now.
Are you familiar with Java?
Many things have remained similar, but especially from the 1.12 to the 1.13 there have been many changes. You can try it, but you will probably run into some problems - unfortunately there are few answers on the Internet for newer versions. Therefore, it is important that you learn to deal with the spigot docs (https://hub.spigotmc.org/javadocs/spigot/overview-summary.html).