The best beginners website it 2KB (2 knotty boys)
They also have 2 informative books with great pics and step by step instructions
I did a rope workshop with them in San Francisco back in 09 and it was awesome
You can download their vids from the website and slowly practice
The thing with rope is if you don't use it you lose it... so practice
And safety is the most important factor
Its very easy to hurt someone and as the "Top" you have a strict duty of care to ensure the "victim" is cared for during and after the tying
Make sure you use good rope , I prefer jute or hemp ... cheap rope burns

And get some EMT shears or something thats going to cut the rope easily in an emergency... rope is cheap... so be prepared to CUT !!
TwoKnottyBoys.com
There are many books available on the subject that can help you learn
Whether your doing it for decorative/arty purposes or just for sex