What is the meaning of catch on fast?

"Catch on fast" is an English idiom that means something like understand or learn something new or adapt yourself in an unfamiliar situations quickly with minimal explanation

It is usually considered as positive as it implies to grasp the new subject, idea, procedure, skill or something at hand quite promptly, with lesser difficulty when compared to others requiring repeated efforts, instructions and time of adaptation.

For example:

- Our child catches on things really fast!