Sorry if the topic is misleading. I dont know how to formulate it correct.
My idea: I have a raspy with a Sim in it. I know how to create a local dashboard with node-red
I want to read a temerpature and if the temperature is bigger than a given value, it should send a sms.
I know that it is possible.
My question rn is: This tool is for a friend. He is not familiar with codig/node-red or comupters in general. I want that he can go to the raspy (connects with a lan cable for example or whatever), opens a URL and can change the phonenumber and the new number is ready to go.
What you described is just a standard dashboard with a text input node for the phone number (I'd use context to save the number). The rest is just the standard flow type to gather the temperature, process it, and send an SMS to the given phone number.
If the raspberry pi is in the local network, it shouldn't be a problem, and you can just add the nodes as usual.
If the server is online, you can work through http nodes and create an API that will return the dashboard, but then you should prepare an authentication system (there is at least one example in the forum).
When you connect a cable from the laptop to the pi, you are asking the pi to act like a bit like router.
So first thing is for you to research how to do that. Not all devices with network cards are capable of auto-switching to direct cable connections. Worse case would be that you would also need a switch into which you plug both the laptop and the Pi.
A standard router will automatically provide an IP address to connected devices. If the Pi isn't configured to do that, you will need to manually set your laptop's IP to something that the Pi can reach. Assuming you've configured a manual IP on the Pi as well, for example 192.168.0.1 with a netmask of 255.255.255.0, then you could set your laptop to 192.168.0.2. Of course, it is easier if you configure the Pi to serve as a DHCP server. If you do, then the laptop should automatically get an address and you don't have to mess with manual settings.
This is all standard networking though, not Node-RED and you will need to do some reading on how to set things up.
As far as node-red is concerned, as long as your laptop is on the same IP address range (192.168.0.2 - 192.168.0.154 in the example given), your laptop should be able to access node-red on the Pi (http://192.168.0.1:1880).