You're not using the right documentation, the documentation you linked to is for the Arduino WiFi library that comes with WiFi-enabled official Arduino boards. You need the documentation for ESP32:
// ----------------------------------------------------------------------------------------------
// ---------------------------------------- STA function ----------------------------------------
// ----------------------------------------------------------------------------------------------
public:
wl_status_t begin(const char* ssid, const char *passphrase = NULL, int32_t channel = 0, const uint8_t* bssid = NULL, bool connect = true);
wl_status_t begin(char* ssid, char *passphrase = NULL, int32_t channel = 0, const uint8_t* bssid = NULL, bool connect = true);
wl_status_t begin();
bool config(IPAddress local_ip, IPAddress gateway, IPAddress subnet, IPAddress dns1 = (uint32_t)0x00000000, IPAddress dns2 = (uint32_t)0x00000000);
bool reconnect();
bool disconnect(bool wifioff = false, bool eraseap = false);
bool isConnected();
bool setAutoConnect(bool autoConnect);
bool getAutoConnect();
bool setAutoReconnect(bool autoReconnect);