So I see you opted for having only 1 install, the online one. That's fine.
In that case, the Drizzle tool has only one purpose: import Myst 5 EoA, Crowthistle, MagiQuest Online, & Cosmic Cosmo ages
When you get online on the shard and let say you want to visit a given age, Gavster age for instance, you just need to link there by a book in your bookshelves or by the restoration links in your Nexus. On your 1st visit, the system will download & install the age for you on your PC. Depending on how many ages you will be visiting I would suggest you to have some free space...
Somewhere age takes around 161 Mb which is the biggest. Most ages will be around 100 Mb. It doesn't seems a lot but if you consider there are approximately 130 ages, the total count is several Gb.