Allow versus limit, deny versus block?

I have an ssh server running on a port other than 22 on my unbuntu box which I connect to via putty from work to tunnel my http and internet traffic through.

Currently I have the port set to allow and I'm unsure what limiting it would do. If there were just two options I'd say limit was closer to closed but I also have the options to deny and block the port which to me seem to mean the same thing but surely can't be?

Can anyone explain the difference between all of them, what I should set my ssh port to and also if it is limited to a certain number of connections per minute will I still be able to connect if someone else is trying to brute force it i.e. if they use up all the connection attempts per minute?

I'm not in work til this evening so I can't currently check the ip and always allow connections to ssh from it.

Many thanks

P.S - where's the manual/guide?