Eddie88“These are two subodinate clauses.”
Yes, that's why they don't form a sentence.
Eddie88 “1) Why are they subordinate clause when they have subjects and verbs?”
Eddie, Eddie, Eddie!!! We've been through this before.
Almost all clauses have subjects and verbs, whether independent or dependent (=subordinate). There is no reason to be puzzled because a subordinate clause has a subject and a verb. This pattern is as common as mud. 
Eddie88 “
What is not a subordinating conjunction, so it can't be a subordinate cluase because of that...
...And the word what, what part of speech is it? ”
Review my previous posts on
fused relative structures.
what is the fusion of that which
what you say/do = that which you say/do
which you say and which you do are relative clauses.
that is the antecedent of which. that which you say/do and its equivalent what you say/do are both clauses that act as nouns so they are noun clauses.
what can be called a fused relative pronoun. It is unusual because both the antecedent and the relative pronoun that refers to it are contained within the same word what.
Eddie88 “So why are they subordinate clauses?”
Because they are not independent clauses. They are just noun clauses -- clauses that act like nouns.
Eddie88 “I know of interrogative pronouns, but I assume WHY is not one, what is it?”
You can call it an interrogative adverb. I think some people do call it an interrogative pronoun, however.
Eddie88 “what a complementiser is”
Basically, it's a word that stands in front of a clause that turns the clause into a noun.
The complementizers in English are that, whether, if, and for.
I know that you have studied hard.
I can't decide whether to stay or to go.
It doesn't matter if you do it now or later.
It's important for you to plan the project carefully.
Some writers include all the interrogative pronouns and adverbs in the complementizer category as well when they introduce embedded (i.e., indirect) questions.
Eddie88 “a modal verb”
The modal verbs don't add "s" in the third person singular of the present tense. They are always followed by a bare infinitive (infinitive without
to). c
an, could, will, would, shall, should, may, might, and
must are modal verbs. These nine are the most important ones to know.
CJ