Underline the adverb clause and what word does the clause modify?

my grandma always yells at me because i only own two pairs of socks.

…because I only own two pairs of socks, would be the adverbial clause (adverb clause).  

An adverb clause is a dependent clause within a sentence that modifies a verb (or a whole clause) to indicate time, place, condition, contrast ,reason, purpose or result, and it begins with a subordinating conjunction such as if, when, because, or although.  

These clauses could be at the beginning, middle or end of the sentence. In this case it is at the end of the sentence and it modifies the verb to yell: My grandma always yells at me, and the reason for this "yelling" is explained with the use of the clause because.

ah, shun the horrid gulf! by scylla fly.