When is it said that you can use try with a Swift error?

I was told that I could use try with a swift error, but when is it said? Isn't it just a guard? I was wondering, but it was a simple matter, so I will record it as a memorandum.

First conclusion

If "throws" is described in the definition method, you have to write the process to receive the error by try.

Example sentence

struct KeychainManager {
    
    private static let keychain = Keychain(service: "com.example.github-token")
    private static let tokenKey: String = "token"

    static func getToken() -> String {
        //The following will result in an error
        guard let token = keychain.get(tokenKey) else { return "" }
        return token
    }

Error statement

Call can throw, but it is not marked with 'try' and the error is not handled

Cause

KeychainAccess

public func get(_ key: String, ignoringAttributeSynchronizable: Bool = true) throws -> String?

When I try to define and jump to the get method of KeychainAccess, the notation throws is displayed. In other words, you have to write a countermeasure to receive the thrown error.

Correspondence

When I used the do-catch syntax, the error disappeared. (You can just try? Without using do-catch, but you should handle the failure.)

static func getToken() -> String {
        do {
            guard let token = try keychain.get(tokenKey) else { return "" }
            return token
        } catch let error {
            print(error)
            return("")
        }
    }