Yoga and Yoke are bleieved to be taken from the same Sanskrit root word, YUJ, I think.
Yoga in relaity is acctualy a word used to name the state of union between God and Man, wherein there is no didstiction between God and the Soul, and idea expressed in the writting of Christian Saints and Mystics, also Jewish, aswell as the Eastern writtings that alot of people know today, and associate this kind of concept with.
So basicaly it means "being Yoked" or "too Yoke" something along those lines, but that is a very literal and dry represenstation.
But it also applies to the method of attaining union, and of this there are many branches;
Hatha = Physical Exercises (asna), Breath Control (prajnayama) mainly,
Karma = Which is the preformence of Good works, Charity, ect.
Mantra = Recitation of Prayers, but also a lot more involved than mearly saying the words.
Yoga is both mental and physical, but as you progress it becomes more mental and less physical, Hatha would be like Kindergarden/Grade 1 or something, getting you ready and comfortable, instilling basic ideas and things that will be used for the reast of your education, not always needed for the gifted, who are far and few between, but a neccesary step for most, then up through to Tantra and Kriya which would be like a Phd.
A little side note, Yoga is attained by completely stilling the mind, which inturn means the breath is stilled, as the two are intimately conected, in this sate of complete reast you merge with ........ and Samadhi or Nirvana is experienced, which is the mearger with what is know as God.
There is much much more, if you want to try something that will help you greatly, keep you attention Focused on the bridge of your nose/in between your eye brows, watch your ingoing and out going breath at this erea, and think of God, that God is with you,
"For he who knocks it will be opened to him"
Also have a look at these pages, they might look a little funny (some of them) but they are amoungst the best organisations that I've discovered,
http://www.kriya.org/
http://www.prajnanamission.org./
http://www.yoganiketan.net/
http://www.yogananda-srf.org/
http://www.ananda.org/
http://www.workofthechariot.com/
http://www.yogamag.net/links.htm
http://www.himalayaninstitute.org/
http://www.swami-krishnananda.org/
(the site for "The Divine Life Sociey" homepage seems to be down at the moment, but Sivananda is one of the great gurus of modern times.)
This one has a whole heap of differnt sites, some of which are above;
http://www.yogasite.com/yoga-orgs.html