You can get THE ssh client from http://www.ssh.com/
SSH is just a program very similar to the telnet program that cones with windows except this one is more secure and easier to use and comes with many additional features like drag and drop file transfer
Assuming you have a login for the macine you want to login to then connect to the server and login. Once logged in type in ps -A (note that should be capital A) to see all processes running. Typing in top will show you more the kind of information you will need to see to determine what process is bringing down the server.
As far as killing processes you won't be able to kill any processes other than your own unless the administrator has given you permissions otherwise.
To kill a process you type kill and the process id such as
If you dont specify a specific signal to send to the process it send the default signal of TERM (ternminate).
You can read more about it by typing in
at the prompt. Linux has an extensive manual so type
and it will display all you need to know.
I wouldn't recommend killing processes if you don't know what you are doing. If you have adminstrator privileges you could end up damaging or taking the server down yourself.