The monitor should fire up and show something. Make sure all of the memory counts and that the floppy drive light comes on one time during POST.
Enter setup by hitting the appropriate key (delete, F1, F10, Esc, or whatever it is) and check the CMOS settings.
Now is the time to change stuff and see if the computer will remember it.
This is where you configure your motherboard's components, peripherals, and controllers. Setup is usually in ROM and can be run by pressing a certain key during POST. If you make changes, you will need to exit setup and save changes to CMOS for them to take effect. You will be able to change the battery backed-up date and time kept by the RTC. Memory configuration like shadow RAM and read/write wait states can be changed from their defaults.
IDE hard disks can be detected and configured. MFM disks can be low-level formatted and configured. Boot sequence and floppy drives can be configured and swapped.
PCI cards and even ISA cards can be configured, and PnP disabled.
ISA bus speed can be changed and ports can be disabled. Yes, you can really hose your computer if you play with Setup! So don't try this at work, kids.
Notes on Setup:
Write down your favorite settings. IDE disks are almost always configured as Auto detect or User-defined type.
Some hard disks bought in a package will be readable and bootable as a type 1 (or some other type) to allow the user to transfer some files to a floppy. Then once you have the files, you will set the drive to its actual type and use the files on the floppy to configure the disk, which is often proprietary drivers.
When changing the ISA bus speed, do not vary it from 7.5 or 8.33 MHz (you will need to do the math yourself), or you may incur some very damaging errors. The ISA speed will be a submultiple of memory or PCI bus speed. PCI bus speed is normally setup using jumpers on the motherboard, and it will typically be one-half of the memory bus speed. 25, 30, and 33 MHz are the only recognized PCI speeds allowed as of this writing. 66 MHz is a future enhancement, possibly available on RISC systems or high-end Intel servers.
Use shadow video unless you have problems. Shadow the ROM of your NIC or SCSI card for better speed.
For better speed and if you have EDO memory, you can usually use the most aggressive memory settings - just try it out before you stick with it to avoid corrupting data files. Much, much more on Setup optimization can be found here.
If your PC can boot and run setup, you're almost done. Now you can begin
to install all of the other components. You should begin to mount the drives
in the case if you have not already done so.