Sets are not parts. Parts are not sets.
But there’s sets with only one part.
As explained, 11025 is the number for the set, so you find it in Sets, and it
contains only one part, which is the baseplate, and whose number is 3811.
Also for single tiles I only see
the 4-5 digit number, where the ones in a Lego manual are much longer?
4-5 digits numbers = what LEGO calls “Design ID,” they (mostly) correspond to
moulds, without specifying a colour.
The numbers at the end of instructions are PCCs / “Element IDs,” they identify
both a mould and a colour.
You can search those on BL, and you’ll be redirected to the part’s page with
a note on top saying which colour it corresponds to, like on the example below.