I'm a newbie programmer with Liferay and Marklogic. I'm trying to connect the MarkLogic using these guides
https://www.liferay.com/community/wiki/-/wiki/Main/Database+Portal+Properties
but to no avail. May I know what kind of database MarkLogic is? and how do I implement the connection?
Marklogic is a NoSQL database and not supported as a backend for Liferay - which you seem to configure it for. If you write your own application on top of Liferay, you are able to connect to any database you like - including Marklogic. It's just not for Liferay's own data.
If you're asking how to build your own application on top of it: That's way too broad for a simple question on stackoverflow.