Answer:
a) The set of real numbers is the union of the set of Irrational numbers and the set of rational numbers.
b) Real numbers have a lot of properties, one example is that they are closed under a lot of operations, like addition or multiplication.
This means that if we have two real numbers A and B:
A + B is also a real number.
A*B is also a real number.
c) A good way to learn Algebra (or math in general) is:
First, read the textbook, have a general idea of the complete topic, if you don't understand something, keep reading, just take note of all the things you don't understand.
Second, ask the things that you do not fully understand, not shame in it, math has a lot of complex relations that sometimes can be really hard to understand, and there are a lot of cases (at least for me) where one can think that understands very well a topic, but it is wrong, so in order to avoid this, ask everything you can.
Third, do a LOT of exercises, the only way in which you can learn to use your equations and relations is applying them in math problems, and it will also help you to understand the meaning of those equations in a more profound way.