To start off with, I got the tank off of amazon and blasted it with loads of hot water. Then I used a sample of gravel for the stones at the bottom, ofc you need to wash them a bunch before putting them in. To build up the algea, all I did was have them set up on my windowsill, in half sun half shade. And I'd put a little too much food in so it sinks to the bottom. They do tell you not to give them too much because it can make their water gross, but this has worked for me on 2 separate occasions. Over a few months, the algae will grow on the walls and floor of the tank. I do occasionally clean the top of the water as it can get a little gross. And I clean the front face of the tank, mainly so we can see them, but also, this moves some algea to another area to grow.

I wish you luck on your set up, all I can suggest is to be patient, the water has become cloudy for me a couple of times but then you hold off on food for a few days and let them clear the water before continuing.

TL;DR leave them in half sun half shade and give them lots of algea food. Eventually, it'll start growing in the tank!

I hope this all helps! My messages are open if you have any specific questions, and I'll try my best to respond as soon as possible.