ESP8266-01 no serial output - arduino

Question

I'm new to arduino and stuff like that. I have an arduino nano and an esp8266-01 (https://www.reichelt.de/entwicklerboards-esp8266-wifi-modul-debo-esp8266-p192142.html). I have the Vcc connected to 3V3 and the ESP GND to the GND of the arduino. GPO0 is grounded and RX of the ESP is connected to the RX of the arduino (Tx to Tx too). I know, that i should use resistors between the RX connections, but when i do that, the esp times out (i guess my usb cable is too long...). I use the version 2.7.4 of the ESP8266 and i can upload without an error.
I am using this example code:
/*
This sketch demonstrates how to scan WiFi networks.
The API is almost the same as with the WiFi Shield library,
the most obvious difference being the different file you need to include:
*/
#include "ESP8266WiFi.h"
void setup() {
Serial.begin(115200);
// Set WiFi to station mode and disconnect from an AP if it was previously connected
WiFi.mode(WIFI_STA);
WiFi.disconnect();
delay(100);
Serial.println("Setup done");
}
void loop() {
Serial.println("scan start");
// WiFi.scanNetworks will return the number of networks found
int n = WiFi.scanNetworks();
Serial.println("scan done");
if (n == 0) {
Serial.println("no networks found");
} else {
Serial.print(n);
Serial.println(" networks found");
for (int i = 0; i < n; ++i) {
// Print SSID and RSSI for each network found
Serial.print(i + 1);
Serial.print(": ");
Serial.print(WiFi.SSID(i));
Serial.print(" (");
Serial.print(WiFi.RSSI(i));
Serial.print(")");
Serial.println((WiFi.encryptionType(i) == ENC_TYPE_NONE) ? " " : "*");
delay(10);
}
}
Serial.println("");
// Wait a bit before scanning again
delay(5000);
}
My problem is, that i get no serial outputs. I read on forums, that i have to use software serials, but it didn't do a thing.
In tutorials (https://www.youtube.com/watch?v=ZJnpgYlelEA) they just connect the ESP and it works without any problems. Can someone please explain this to me?
Thanks!