Difference between Ranking and Rank()

I am trying to implement "Ranking" but because of lack of knowledge instead of using Ranking option I used Rank() function and after a while I realised that both are different.

I was able to understood below points:

Rank() : This function can be applied on Dimensions where dimension can also be a text field.

Ranking: This option can only be applied on Measeures and can't be applied on dimensions/

Now my query here is what is the difference between both Ranking and Rannk().

Can anyone please educate me on this.

Thanks for your time.

Siva