- $b is an object, which is an instance of a class. PHP doesn't have strong data types so there's no way of knowing by just looking at the code.
- options is an array in $b, and you're referencing the key "somthing".
- Yes, and inside the class, you have to use $this due to crappy scoping.
PHP has a broken, half-assed-implemented OOP model. If you really want to learn how OOP works, Java is the way to go.