Here is how you should consider that sentence grammatically:
{ [ ((先ほど)お) (渡し) (した) ] [初心者セット] } (が) (きっと) (お(役にたちます))。
{ [relative clause] [noun modified by the relative clause] } (subject marker attached to the noun) (adverb) ((honorific prefix attached to the main verb predicate) (main verb predicate in the formal masu form))。
Breaking down the relative clause: [ ((先ほど)お) (渡し) (した) ]
[ ((adverbial noun)(direct object marker attached to the adverbial noun)) (subject of the relative clause) (predicate verb of the relative clause in past informal form) ]
Here are links to help you out. You’ll also need to be able conjugate into the past informal form and to identify the parts of speech of all of these words (http://www.jisho.org helps) in order to learn how to deconstruct these clauses yourself.
https://en.wikibooks.org/wiki/Japanese/Lessons/Relative_Clauses