There is no set of rules about what a girl (or boy) is supposed to do when her partner stimulates her (or him), manually or orally or in any other way. During Sex, you can do anything that feels right, you can be silent or loud or talk or laugh or cry or move a lot or very little or show your partner what you like and do lots of other things.
I'm not sure whether this is specifically about you, but just in case: Hon, let me be blunt, really, IMHO, If you're wondering "what to do" when your boyfriend stimulates you manually, it sounds to me like you're just not ready for that. - Everyone is different in his/her sexual response, and no one here can tell you "what to do" - it should come naturally and if you have to think about what to do while he is doing something which is - after all- intended to be pleasuring for you, your response most likely won't be natural at all.
Maybe it would be good if you thougth about whether you're already ready for partnered sex yet.
“...i'm just trying to find
a decent melody
a song that i can sing
in my own company...”