Syncs
Having manually added a Series to TitleCardMaker, it should be obvious this will be tedious for any more than a handful of Series. This is where the idea of a "Sync" comes in.
Syncing allows Series to be automatically added to TCM. You can Sync from any non-TMDb/TVDb connection, each Sync can be customized to only add filtered subsets of your Series, and can also automatically assign specific Card customizations through Templates.
For most users, I recommend Syncing from Sonarr. However, if you are not using Sonarr, then your primary Media Server is the next-best option. You can use the sidebar to navigate to the instructions which suit you.