What the Create Date of a file is, is actually rather self-explanatory. It is basically just the date of creation of the file in question.
The is often displayed in the date format given by the computer, device or machine that created the file. In some cases, the time of creation is also included in the Create Date, but in some cases, it may also be separately stated in the metadata of the file.
Create Date can (but doesn't have to) differ from the date the file was last modified. While the latter always stores the last date of modification of a file, the Create Date always stays the same.