If you're gonna try to put your load on a specific face then you should apply the following GUI command:

Main Menu -> Preprocessor -> Loads ->Define Loads ->Apply ->Structural -> Pressure -> On Areas.

in case of body load type(for example :Temperature ,Heat Generation ..etc) you can use :

Main Menu>Solution>-Loads-Apply>load type>On Volumes

thank you very much , I will do .

Hello,

does anyone know how to apply a length-varying axial load on a bar in ANSYS? Can I define the function load?

Yes, you have to define your load function. The link below illustrate a simple one:

https://www.youtube.com/watch?v=CIIDSS06cQs.

Best