SharePoint sites vs. Site Collections - CONFUSED!

All,

Tried following in a trial O365 (E3) account (tenant name: "blithe1"):

1. Created 2 additional "collections', in addition to main site collection :

https://blithe1.sharepoint.com <-- 'ROOT' collection created by default 
https://blithe1.sharepoint.com/teams/Collection-1 <-- Created new collection with "../teams/.."
https://blithe1.sharepoint.com/sites/Collection-2 <-- Created a new collection with "../sites/.."  

2. When we see the properties of each of above collections then it shows that it has "1 subsite". I think this is for the "Home" site of that collection (i.e. the above URLs themselves).

3. When we log into Office-365 and select the SharePoint "TILE" then it directs to:
https://blithe1.sharepoint.com/_layouts/15/sharepoint.aspx <-- This is not a "site" since the gear icon doesn't have "Site Setting" option etc

4. Here when we click the "+ Create Site" it asks for "Team Site" or "Communication Site". I created "Team Site" and site name as "PSO".   It creates a site with URL https://blithe1.sharepoint.com/sites/PSO

AT THIS POINT IT DOES NOT GIVE US ANY OPTION TO SELECT SPECIFIC COLLECTION TO CREATE THE SITE IN. When we go to our three site-collections one-by-one and see "Site Contents" then none of the collection lists this "PSO" as a "subsite", so it's effectively not in any collection (and is obviously not a new collection in itself since it's not listed in collections list).

5. Next created a subsite under the "root" collection (by visiting collection-URL, then gear icon "Site Contents" and click "+ New" and select "Subsite"). 

URL (Fixed part): https://blithe1.sharepoint.com/
URL (Editable) : /Subsite-in-Root-Collection

It created the subsite and directed us to URL:
https://blithe1.sharepoint.com/Subsite-in-Root-Collection/SitePages/Home.aspx

5. Similarly created a subsite under "collection-1":
URL (Fixed part): https://blithe1.sharepoint.com/teams/Collection-1/
URL (Editable) : /Subsite-in-Collection-1

It created the site and directed us to URL:
https://blithe1.sharepoint.com/teams/Collection-1/Subsite-in-Collection-1/SitePages/Home.aspx 

So from a "non-developer" perspective with no knowledge of actual low-level coding and structure of collections etc. it seems like all Site-Collections by default have a "HOME" site created (and with a set template "Project Site", "Team Site" etc). In case we don't intend to create additional sub-sites then this HOME site itself can serve the complete purpose. A collection is site itself and everything else is SUBSITE because home site (https://blithe1.sharepoint.com/teams/Collection-1/SitePages/Home.aspx) will contain all the subsequent sites in that collection (https://blithe1.sharepoint.com/teams/Collection-1/Subsite-in-Collection-1/SitePages/Home.aspx)

However rebellious it may sound, from a "non-techie" view, the "collection" may be just a "terminology" in SharePoint, it's actually just SITES and SUBSITES. In fact the collections like any other site also has users and permissions with names like "Collection-1 Visitors", "Collection-1 Members" etc.

One-Drive (https://blithe1-my.sharepoint.com/) listed as site collection, may be another special site providing ability to everyone in the organization to create their own quick "folders" in this site and able to share among each other.

Ofcourse there are other state of the art stuff in the actual features in these sites/subsites like "Flow", Power BI, External Data Sources, MetaData etc.