The cables that definitely need to be connected are the 24pin which powers the motherboard, the VGA cable which powers the GPU depending on the slots (it may need a 8pin + 6pin or two 8pin), the CPU cable which will power the CPU and SATA power cables which will power the HDDs and SSDs. In addition to that, a cable for each of your HDDs and SSDs will be needed to be connected from the drives to the motherboard's SATA slots. That's about it for the PSU and then you have the motherboard. There are fan cables and stuff there too. I recommend opening your motherboard's user manual and see what goes where.