yes to the first. to the second, yes and no both.

to outrageously oversimplify, a disk partition, or partition for short, is simply a separate region on a storage disk (which can be anything, whether it be your computer’s hard drive, a USB drive, an SSD etc).

you can shrink, expand, delete and create partitions according to your will (as long as you have enough space on your disk). space on the disk not belonging to any partition is called unallocated space.

it is necessary to have your disk structured into multiple such partitions ¹ to install multiple operating systems on a single disk (in fact, most OSes use multiple separate partitions on the disk by themselves² ).

dual booting is simply when you have multiple operating systems running on the same computer. if you’re going to have both of them installed on a single disk, then sure, you’d need to create separate partition(s) for the new OS.

and by “you” i don’t mean you manually do it. for practical purposes, basically all the linux distros these days have an automated installer which can detect what OSes (such as windows) are already on the disk, and will automatically create the required partitions in the unallocated space available, and install the OS in those (when it asks you about where to install to, just select the option named something like “Install alongside Windows”). there’s really no need to dick with the partitions manually as a beginner when your distro’s installer will take care of that for you, except maybe if you want to create space for linux to install itself to³.

so, the answers are:

1 - yes, creating a new disk partition and dual-booting are two separate things.

2 - could you install for dual boot without creating a partition in the process? not really, as fundamentally operating systems, whether windows, linux or anything else, need to be installed to partition(s) on a disk. it’s just that the OS’ installer usually does all the partitioning for you

2.1 - could you dual-boot without manually creating a partition, or touching partitions in any way? sure. if you’re installing an OS to a separate disk for example, you could let the installer simply overwrite, repartition, and install to that disk and run both OSes off separate disks on the same computer.

if you’re installing both OSes on the same disk, then you can also usually let the installer take care of installing linux alongside windows without a problem. the only thing is that if you don’t have enough space as you’d like for the linux install, you may have to resize your windows partition yourself to create more.

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notes:

(this is all stuff you don’t really have to care about right now! (though you may want to read no. 3 later on, when you’re actually installing linux on your main system.) it might confuse you more than helping, and it really isn’t required for you to understand, but read on if you’re interested)

1:

here is an example disk layout on a disk that has both windows and linux installed. to learn about the structure of your own disk (if you want to), on Windows you can fire up the preinstalled utility Disk Management and have a look.

2:

a modern Linux installation, for example, usually has the following on your disk:

• an EFI system partition (contains stuff required for the computer to boot the OS partition)
• a main partition where the actual OS and data is
• optionally, a swap partition
• some people also prefer to keep a separate partition for their /home/ directory (the folder that contains all your user account’s data, separate from the OS and the programs installed on it), which is useful (among other things) to install a different Linux variant on the OS partition, while keeping all of their user data and seamlessly using it with the new installation.

a standard Windows installation also has multiple separate partitions on your disk (apologies for not finding a better source but this details them well enough).

3:

the only scenario in which you might have to touch the partitions yourself is if your disk doesn’t have enough unallocated space to comfortably use a linux install. (as a comparatively lightweight OS, even the very heaviest variants of linux shouldn’t go over 4GB in terms of space strictly needed for installation, but you also need some actual storage space to have your files and stuff in lol).

in such a scenario, you could shrink your main windows partition if there’s enough space (Explorer should tell you how much free space you have). for example, if your windows partition is 300GB but it’s only occupying 200GB of space, you could shrink the windows partition down to 250GB, leaving 50GB of unallocated space on the disk for linux partitions.

to do this using the preinstalled Disk Management utility on Windows, right click the Windows partition you want to shrink (whether C:/, D:/ etc.), select Shrink, and follow the instructions. please be sure to select the right amount of space to shrink it by according to what you want, and confirm again that it’s correct.

please exercise care, as messing up your disk partitions could royally screw up your OS. what you’re doing here can’t really hurt anything, but make sure to follow the instructions carefully. if possible, back up all your important data before attempting this.

once you’ve got what you think is the adequate balance of Windows and unallocated (soon to be Linux) space for your needs, boot into the distro from your usb and let the installer take care of the rest.