In Raspian Jessie it should be activated allready. If not enable the SSH server by opening the raspi-config:

$ sudo raspi-config

In 8. Advanced Options you can activate SSH.

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Look up your gateway:

$ netstat -r -n

Find you IP address:

$ ifconfig

or:

$ ip addr

Give the Raspberry Pi a static IP address. Open the interfaces file:

$ sudo nano /etc/network/interfaces

Add these lines:

  # Ethernet
  iface eth0 inet dhcp
  allow-hotplug eth0
  auto eth0:1
  iface eth0:1 inet static
    address 192.168.0.199
    netmask 255.255.255.0
    gateway 192.168.0.1

Or:

  # Ethernet
  allow-hotplug eth0
  iface eth0 inet static
    address 192.168.0.199
    netmask 255.255.255.0
    gateway 192.168.0.1
    dns-nameservers 192.168.0.1
    

Save and quit, ctl+o, Return, ctl+x.

Disable the DHCP-Client:
In Raspbian Wheezy:

$ sudo service dhcpcd stop
$ sudo update-rc.d -f dhcpcd remove

In Raspbian Jessie:

$ sudo service dhcpcd stop
$ sudo systemctl disable dhcpcd       
     

Restart ethernet:

$ sudo ifdown eth0:1
$ sudo ifup eth0:1

Or/and reboot:

$ sudo reboot

One can login from your computer with:

$ ssh pi@192.168.0.199

or with XWindows support:

$ ssh -XY pi@192.168.0.111

PW: raspberry
Or install an VNC server: VNC

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If the host key verification failed, one can remove the old key with:

$ ssh-keygen -R 192.168.0.123

And with

~.

one can terminate a broken ssh session.

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