Having trouble with Volt Specter fight, please help

So I'm brand new, not only to warframe but to shooters in general. I've been having fun, but the volt specter at the venus junction is just kicking my ass consistently. I don't know what to do about his shield, how to do any real damage to him, i only managed to get him to about 50% health at the lowest.

I'm so sure i'm doing something wrong, but i have no clue what. I picked Mag as my starter frame, but her abilities don't seem to be helping much?
anyway pls help