While you can only have four characters in your party at any one time, this does not mean that your other characters will be sitting around doing nothing. You can send them out on expeditions, gathering up resources and giving you a decent passive income.
You will get access to Expeditions at Adventurer Rank 14. When it is unlocked, you can visit the Adventurer’s Guild in any city and speak with Katheryne. The Adventurer’s Guild will be marked on the map by a small compass icon. Select the “Dispatch Character on Expedition” option, and you will be brought to a screen showing a map with some icons on it.
There will be two maps, one for Mondstadt and one for Liyue. Each Expedition will result in different rewards, and you can see these by hovering over it. Finally, you can set how much time you want your characters to go on the Expedition for. The longer the journey, the more of each type of resource they will find.
Keep in mind that any character on an expedition cannot be used in your party for the duration, so don’t send your stronger characters. If you how unleveled characters, this is a perfect way to use them as they will not be in any danger. Some characters will also have bonuses for certain Expeditions, so make sure you experiment with who you send out.
There is a limit to how many characters you can send on an Expedition, but this will increase as you increase your Adventurer Rank. Expeditions are an excellent way to get certain annoying resources, so make sure you always have characters that you don’t need in our squad out hunting down the materials you need.