you don't need an image to understand clustering, you can google the images if you want, you'll find plenty of them
Basically, topic clustering (aka keyword clustering, aka pillar content, they're basically the same thing) means silo (or site structure if you prefer)...
And most clusters (silos) are just pyramids of pages, something like this...
TOPIC PAGE > Sub-topic page > Sub-sub-topic page > Sub-sub-sub-topic page... etc...
Although, to be honest, for small / medium size sites (sites with dozens to 100s of pages, that's what I call small / medium size) clusters are only 1 level deep usually (so, TOPIC PAGE > Sub-topic page, you almost never see small sites with content that's 2-3 levels deep)
For example, let's say that your site is about cars, and the 3 most important keywords that you wish to rank for are:
- car parts shops
- car care services
- car retailers
You find these 3 keywords that you really like and then you plop them into Ahrefs / Semrush (or whichever keyword research tool you use) and - to your disappointment - you see that all 3 these keywords are very hard to rank for (they have high search volume and high keyword difficulty, something like 50+ KD score in Ahrefs).
So what do you do in this case when 1 single page on each keyword might not be enough to rank you because of the high competition (remember, in SEO high search volume is almost always equal to high competition regardless of what the SEO tools say)?
Well, you use keyword clustering (siloing, topic clustering, etc... again, these terms mean the same thing more or less, so I'm using them interchangeably in this post...
So, you use each one of these keywords as topical clusters by making one "pillar page" for each keyword (just like you would normally do anyway for most sites), but instead of making just 1 page for each keyword like you would normally do and then build links to that page you are instead making one page for each keyword, but then you go back to Ahrefs / Semrush and find at least a few more keywords that are relevant to each topic and write content on those keywords too and link to the page of the main keyword that these relevant keywords support.
Something like this...
car parts shops > car parts shops by location
car parts shops > car parts shops by car make
car parts shops > car parts shops by component
car care services > car painting services
car care services > car washing services
car care services > tire changing services
car care services > oil changing services
car care services > engine checking services
car care services > car maintenance services
car retailers > car retailers for used cars
car retailers > car retailers for new cars
car retailers > car retailers for sports cars
car retailers > car retailers for limos
Of course, these examples might look a bit silly because if intend to have a page titled "Car Parts Shops by Location" you're not going to turn into a stupid blog post talking about locations for car shops. You can still do that if you want (you'd probably even find enough info to make a decent post), but you would not fulfill the intent of the keyword because people who search for car shops and mention the word "location" in their search are almost guaranteed to want to find actual shops in whichever location they're searching for.
So, in this case, both google and your users would love if you'd put a map or something on this page, that let's people find car shops in the location of their choice instead of boring them to death with information about car shop locations
So yeah, use your common sense and judgement when you come up with the right silo for your site and the right structure and clusters for your content and you'll be able to make a great site... hopefully...