Starry Gem Usage Question - New player

Sorry if dumb question. I am new and have tried to find a comprehensive guide regarding starry gems but most videos assume you have baseline knowledge. If I have prism starry gems, I should convert them in AH? I cannot do that yet because my account is new but hoping I can soon. Then I can either buy cheap C copies and retire to get contract gems or save them to buy a cheap B copy? I am guessing for a new player its better to retire heroes for the contracted ones so I can use those in events? From what I see, I need the bound/contract ones in order to be able to buy the starry gem value packs from limited events tab. Pls lmk if I am missing something bc most guides arent super noob friendly