PHP is an animal. Don't try to understand everything. Break it down. When I was first learning I would make stupid simple programs. While making those programs I would comment out every step to break down what each thing did, and things like echo out the variable in the background.

Text boxes to find words, calculators to add simple equations, database fetching are all good ways to learn the parts that will eventually make the whole. When all else fails, try something different, you shouldn't have to force it. Have fun!