Actually it is simple: I have connected a Raspberry Pi with Raspbian OS to the ethernet port of my notebook running Kali Linux (based on Debian). Now I want to ssh into the Pi, but I do not know the IP of the device.
Run arp scan of local area network and connect to you RPi IP adress which you can find by searching for RPis MAC adress. Code looks exactly like
sudo arp-scan --interface=eth0 --localnet
If you donot have this package, install it by
sudo apt-get install arp-scan
I have been in this exact scenario before. Luckily, I'm friends with my high-school's IT guy, and he helped explain it to me.
Ethernet cables have 8 pins (copper wires), each designated for a specific purpose. Namely, 2 cables: Data-in and Data-out. The problem with connecting 2 devices directly via a single Ethernet cable (I call this set up P2P Networking and use it often) is that they both try to take data in from the Data-In pin and send data to the Data-Out pin. They're listening to them listen to eachother and they're both trying to talk at once, and it's simply not working. This where where RJ45 Crossover Cables come in.
A crossover cable is a specialized Ethernet cable specifically designed for 2 devices to be connected directly. You can buy them from your local shop, or you can make them (which takes a few more tools, but you already know how to swipe a debit card, you don't know how to make them). You can learn to make them here
So assuming that you've made one now, there is the IP issue. Once connected, your Raspberry Pi will probably ask for an IP address from the only source it has: You (AKA the computer you've connected it to directly). You must be running a DHCP server listening on your eth0 (or eth1 or whatever you have for Ethernet) port.
This is relatively easy once you get it set up. Whenever you want to connect to the Pi, you'll just start up the service (I have to assign an IP to my ethernet port via ifconfig eth0 192.168.1.1, but I think that's just because I set it up wrong) and connect it, then you can run an nmap scan and find it.
Learn to set up isc-dhcp-server here