Hi!
Here are my hints …
User:
1º It’s important to enumerate in this box, but Dirbuster won’t lead you where you need.
2º When you are starting with one HTB machine, it’s a good practice to try the Vhost (name of the machine) + .htb. In some instances, you might get additional Vhosts which are worth checking as well.
3º If you arrive to a login page, you are on the right path.
4º The mango is a word play related to the technology to research. Mango is not a mango, but is close to it.
5º Once you figure out the technology, research how you could exploit it. There are different articles on the Internet. One of those articles will give you an idea about how to proceed further.
6º My advice would be to play first with burp and the repeater, in order to get a slight idea about how to design your attack. Then, create your own script. This was the best part for me.
Root: Basic enumeration. It’s way easier than user, and I am sure you have solved other machines this way.
Thank you @MrR3boot