shields

Not sure if this is the right forum as i'm new to KSP. So i have the problem of where after my initial burn stages, my other engines that i would use to further push my ship into orbit and any further are empty.. No liquid fuel.. what am i doing wrong exactly?? i load the ship up with many fuel sections but clearly i'm doing something wrong, recap i'd like some help on how to manage my fueling so i may venture further and stop this issue from occurring when i'm switching stages. Thanks heaps!