How to share classless networks using VLSM?

Question

Computer networks

Good evening!
I can't figure out how subnetting works.
Let's start with Classful (class) & Classless (classless) addressing. Classful addressing refers to the division of the entire available range of addresses into classes. For unicats, only A (1.0.0.0-126.255.255.255/8), B (128.0.0.0-191.255.255.255/16), C (192.0.0.0-224.255.255.255/24) are used, I don’t take others into account.
Classless addressing introduces concepts such as CIDR (described in RFC 4632) and VLSM. Odom wrote about VLSM like this: " VLSM masks are used in cases where it becomes necessary to use several different masks on different subnets of a separate class A, B or C network." It turns out that this mechanism is used only for masks that are not less than class ones.
For descriptionCIDR uses the following description: "CIDR routing is a global address assignment convention that defines how the Internet Assigned Numbers Authority (IANA), its member agencies, and ISPs allocate globally unique protocol address spaces. 1Pv4 to individual organizations." It can be deduced from this description and from the RFC that variable-length masks are executed for subnetting.
If you describe how I understood the term CIDR and VLSM, then you get the following:
CIDR is a description of what can and should be divided into networks not by class, but by needs.
VLSM is a way of dividing classful networks into subnets.
As a result, the following questions arise:
1) Why should VLSM only apply to class networks?
2) Where is the mechanism of subnetting of networks with a mask less than the class one described? For example, if I want two networks of 200,000 hosts from the 12.1.1.1/7 network, then what mechanism is used here?

Answer 1

network classes are history. Now there are no systems and equipment left that allow you not to specify a network mask and determine it by class.
Now, when setting an address, it is always considered with a mask.
So read about the classes, remember that it used to be like this, consider this the recommended default mask, and read more about CIDR