What terms do I need to use to search for human males fucking mares, alien females, female robots, and female animals in general. I am new to the site and love some help please. Thank you for the help.

male/female human_on_anthro, male/female human_on_feral, male/female human interspecies, or male/female human ~horse ~alien ~robot.
The "~"s in the last query means that we don't need a horse, alien, and robot all at the same time, just one or more of them.
We don't tag genders and species together, so you're gonna have to put up with results that include male nonhumans on female humans.

The male/female tag is a good place to start. The male_on_feral, male_on_humanoid and male_on_anthro tags are good to add, too. Searching for human male/female ~male_on_anthro ~male_on_feral ~male_on_humanoid will give you good results. The size difference related tags are undertagged a little, but can still be of some help. If the non-human partner is smaller, use larger_male or smaller_female. If the non-human partner is larger, use smaller_male or larger_female.