When you find a plugin you like, you can download the file for it. To get Nukkit plugins, you can visit the website - You can search for plugins under the Nukkit category, and also find plugins based on Most popular, recently reviewed, and authors. To get PocketMine-MP plugins, you can visit the website - You can search for plugins by Author, search in categories, and in API versions. The software we will cover in this article for Java. The software we will cover in this article for Bedrock.
There are different software for Minecraft servers, and each software has different plugins, and places to find them.