How do I boot off the MBR? Is that the second option that comes up that says “Failsafe” on boot?
No, you’d then already be beyond that stage. It’s a general setup question during boot loader configuration, controlling where the boot sector is placed.
Can I use commands at that point? Is there a command like FDISK in windows?
Not in the sense you’re asking: You’re talking to the boot loader program at that point, not to some Linux shell. All you have are the commands offered by the boot loader, i.e. to manually alter the boot process for this single run.
You’d typically boot a recovery system, i.e. from a Linux installation DVD, to get a shell that can access and alter the contents of the installed system.
If I delete all existing partitions won’t that delete the OS version that is currently installed?
Yes, it’s the same as with MS Win. The problem is, when the disk is already fully allocated by the existing partitions, you’ll need to make room… there are different ways to do so. Many of then require at least mid-level admin knowledge to know what you’re doing, even if the tools pretend to cover for all that… if there’s just the slightest problem, you can easily make the current installation unusable. And if you don’t care about that, well, then just re-install and partition correctly during the install process
Will I need to re-install after partitioning?
Basically, it depends If you delete partitions without taking special measures, the content is gone. So if you delete system partitions, the installation from there is gone. If you’re just adding new partitions in previously un-allocated disk areas, then no reinstall is required.
Assuming you have enough unallocated disk space, you could
create extended partitions as needed
from your point of you, these can be mounted like “basic partitions”.
As you already know, you can have four basic partition entries, one of which can be of type “extended partition” and gets sub-partitioned.
accordingly, basic partitions are referenced by the numbers 1 to 4 (/dev/sda1, sda2…) while extended partitions start at “5”, no matter how many basic partitions there are