Ratio, Proportion, and similarity

[Ranger1029]

In My school geometry class we have been doing ratios and overlapping triangles and all the stuff to do with proportions and the angle angle therom and what not. That part is understandable. But i cannot grasp how to set up the propertions correctly or solve them. for example in a triangle there is a median, I'm guessing. Well lets say it is a median, or actually i think its an altittude. so the larger triangle of the entire thing has one side given to us known as 24. but there is a division by a smaller triangle we need to figure out represented by x. and the other side, which is the only common value among the two triangles is 10. So how would you set it up? or you could use another more in depth example to explain this concept to me? please.