To start emulating Nintendo Switch games via Eden, you will need
At the time of writing, Eden supports Nintendo Switch firmware up to version 19.0.1. You need to make sure the encryption keys and the firmware files are for the same version.
You can get the encryption keys from Prodkeys. Choose Yuzu on the main page, then choose a version of the encryption keys. Put the keys into the ~/.local/share/eden/keys folder.
You can get the firmware from Zoria's repo. Install it via Tools > Install Firmware in Eden.
You can get the games (in either NSP or XCI formats) from NXBrew.net. Put the files in the application folder that you chose in Eden.
To install DLCs or updates, use File > Install Files to NAND dialog in Eden.
To install modes, choose Open Mod Data Location in the per-game context menu. Put the modes (as directories) in that location.
To enable/disable DLCs, updates, or modes, access the Add-Ons tab in the Configure Game dialog in the per-game context menu.