Can someone explain bloodlines to me, in reference to usurpation and kingdom political power?

Howdy! I'm new - ish, it's only been 40-50 hours, and apparently that's still noob in this game :D - and I'm stuck. Bloodlines have me confused beyond all belief.

So, i'll give the basic story, and you guys can use it as a way of explaining how to solve the situation. Don't just try and solve my situation, but use it as a drawing board to explain how these things work as a whole. Thanks!

So, I'm the Duke of York. Through being a general dick, I hold the midlands and, well, central England. I hold about 7 territories in central England, the top 3 of Wales, and have twice the land of the King of England.

I contributed the most to the rebellion that saw this King seated, and as such, he's quite fond of me, granting land and titles. I want his throne.

I want to know exactly how to set myself up for taking a throne. My initial idea was a faction, but I can't make one. Do I need a pretender position to set up a faction to take a throne?

My second plan was usurping the throne. What do I need to claim power over my King?

Third plan was marriages and making myself heir. How do you marry/get kids/assassinate to twist a line of succession into your hands?

Thanks! I'm off out for an hour or two, when I come back, i'll read the answers and trigger questions. I don't want to solve my situation, I want to be able to use the knowledge to answer any of these situations in the future.