The most important thing you should know about fdisk is, that you probably should not use it.
cfdisk (and parted too) is easier, less error-prone and (like fdisk) not bloated in any way, compared to all GUI partitioning tools.
To use cfdisk, just run:
cfdisk /dev/sd[x] (sda for first harddrive, etc.)
and you can control the tool with your cursor keys!
There are hardly any thing you can do wrong here except accidently deleting partitions (in which case you can just exit without saving), just remember to use partition type 83 for normal Linux partitions (82 for swap) and that you should set the bootable flag for /boot, since a standard-conform BIOS will look there for a bootloader (first).